Many projects after the ICO did not even start listing on the exchanges or postponed it, knowing that as soon as the listing appears on the exchanges, the price of tokens will fall.
It is a very big problem that after ICO projects do not start the listing on the exchanges and investors can not sell tokens.
If there is no listing after ICO investors cannot sell the tokens of the project. If project has a platform, they can use tokens on the platform. But usually such projects does not have a working platform at all.
If there is listing it is very important to see the volums of trade. Because if there is listing but no trade volumes investors can not sell their tokens because nobody will want to buy tokens.