Should I avoid testing unnecessary equipment?
The best practice is to pre-flight everything for every flight:


If you have different pre-flight procedures for different situations then sooner or later you'll use the wrong one and miss something that you should have found. Consistency is really helpful in procedures.
Even if something isn't needed for the flight, checking everything gives you an accurate picture of the state of the aircraft. One broken light is probably just a light bulb, but 3 broken lights and inop pitot heat may be a more serious electrical problem. If you don't know the state of the aircraft then you can't make informed decisions.
Plans change. You might set off for a day VFR flight on a clear, sunny day intending to be home hours before sunset. But if the weather changes quickly or you get delayed then your flight home might have to be night VFR or IFR. If you have equipment issues that restrict your options then it would be best to know that before you depart.


There's nothing wrong with flying with inop equipment provided that you know about it, you've complied with the rules in 91.213 on minimum required equipment and deactivating and placarding, and you've made a conscious assessment of the risk. But not inspecting the aircraft properly or deliberately ignoring inop equipment is a really great way to put yourself in an "up there wishing you were down here" situation.

And from a regulatory point of view, if you don't preflight properly then you're probably in violation of 91.103 ("become familiar with all available information concerning that flight") and of course 91.13 ("No person may operate an aircraft in a careless or reckless manner").