Questions about research assistant posts
Q1: Is it weird or stupid to apply for a research assistant post at some university or research institute, and not a company in industry, with the purpose to gain research experience to boost profile for graduate studies, and why/why not?


Not at all. In my field (biology), this is quite common, the only reason not to do it is that you think you can get admitted without it and are trying to save time. However usually the experience is also very valuable in learning what research is like and whether you even want to do it, or whether you like the field. In other STEM disciplines it also seems to be very common. I've heard of it happening in social sciences (psychology, sociology, history) as well, but I'm not sure how things are exactly there. Usually it's up to the PI if they want an assistant or not. There is a lot of variation there. Some PIs love it, some have zero interest. But there's no easy way to tell, and asking rarely hurts.

You should absolutely mention future grad school plans, firstly because many PIs strongly prefer people who are planning to go to grad school (they're seen as more motivated, there is less commitment as opposed to an indefinite employment contract, and hiring assistants in this way is seen as part of a professor's responsibility to future generations). I am not sure if the same can be said for people who seek similar posts in industry - most of my personal acquaintances have worked in university or national institute labs, not in companies. However, honestly it would be naive in this day and age for a company to expect 22 year old BS grads taking a lab tech position and be fully committed "lifers" - and if they really want you to not run off to grad school after a year, they should put it in the contract.

I'd say it's very different from a baby version of a postdoc. Postdocs are often expected to independently come up with hypotheses, design experiments, locate and order equipment/materials as needed, write grants and submit manuscripts to peer-reviewed journals. Rarely they may also teach and mentor others. As an assistant you will most likely be part of a postdoc's project - duties may range from mechanically doing some simple technique over and over (like running gels or feeding mice) to semi-independently doing a small part of the postdoc's project under constant supervision (but ideally you would always be expected to demonstrate good understanding of the science in discussions, even if you are doing pretty monotonous experiments). You may be expected to help write small parts of the paper, such as methods sections for experiments you did. Should you end up with a PI who encourages independence, you might design experiments or even provide feedback on equipment purchases, and if you are really lucky and hardworking you may even have the opportunity to submit a first author paper. But that would be exceeding everyone's expectations; needless to say, it will look very good on your application.


  Q2: Who are the usual applicants of research assistant posts?


I can't say for sure since I've never been in a position to hire such people. But based on experience and what I heard, the vast majority are either undergraduate students or recent grads planning to apply to a PhD program. Sometimes there are premeds but academics look down on them. There are occasionally people who don't necessarily have future plans, and are just curious about science, or maybe they want to do something related like patent law and decided to get a taste of what it's like in the trenches. I've never heard of anyone doing it just to pay bills, those people will usually have very long term positions (which may sometimes be called "technician", "scientist" or "assistant" etc).


  Q3: What's the difference between a research assistant post and an internship in industry?


Interns are usually expected to be short-term (3-6 mo) and part-time (&lt;20 h/wk). The internship will often be coordinated with the university, and may be required to complete the degree, and result in a grade or certificate. These days governments try to crack down on unpaid work, but in practice there may be an (arguably unethical) expectation that interns work for free. Assistants should be longer term (>1 yr) and paid (and thus officially employed and eligible for benefits - interns sometimes "just come"). But the terms aren't too reliable - the goal of the posting is usually marketing first, accuracy second.

The linked post is for an MS student, those can often become involved in their PI's side-ventures depending on how things go. Usually it wouldn't apply to assistants both because their contribution is smaller, they are less independent, and they will soon begin a PhD program where they will be too busy to follow up. It can happen, though, if the professor really likes the assistant and the assistant isn't totally committed to going to grad school right away.


  Q4: To confirm, if research assistant posts are indeed on temporary contract or short-term, is there indeed a risk for someone to quit their regular full time industry job hoping that a research assistant post will boost their grad school application profile?


Anyone can quit a job any time. Nobody can make you show up. That's one of the few aces employees have in their deck against employers. However, grad applications give a lot of weight to recommendations. The experience you have won't be as well regarded if there isn't an accompanying letter from your boss praising you to the high heavens and saying in detail what a great job you did and what a golden grad student you would make. Obviously if the boss is pissed off at you for quitting out of nowhere, obtaining the letter might be an issue. However, if you worked with your boss on this, discussed your plans ahead of time, did whatever you could and the boss was still unreasonable the admission committee might take that into consideration. Sometimes there are people who did a stint in a lab and did good work but for some reason their supervisor really didn't like them so when they submit the letters and none of them are from this place they worked at. Then you have to sweat a little explaining all of this in a positive way while writing your SoP and other materials, bragging about how great your experience was but at the same time stepping around the fact that clearly you got your boss so mad you couldn't even get a letter from them.