How does exactly ICO work? What the advantage of ICO for companies? All I know about ICO is that some companies make their own coin and then those coins are bought by investors. So looks cool :) But why the companies should be happy if they will have more investors which will be buy their coins? How will companies get that money from investors?
Cryptocurrencies, and by extension issued tokens, live in a legal grey zone.

ICOs are just a means to use blockchain-issued tokens as a funding mechanism. If it weren't for the legal grey area, it seems to me that they're exactly the thing that investor accreditation laws are intended to prevent: raising money from people who are vulnerable to being scammed.

From what I've seen so far, almost every ICO is just lots of talk, without any indication that there is a plan or competence to implement anything but the off-the-shelf ICO smart contract. In other words, a modern incarnation of a pump-and-dump scam.

So to answer your question: the advantage is raising lots of money quickly, without needing to follow up on any promises.

I believe that ICOs are putting the whole ecosystem in a bad light, and are likely to result in legal problems.