I would not encourage anyone to participate in them. It's just a marketing stunt.
Yes , the fact is that the CEX may choose not to list the coin or token after their previous claims of listing the coin at the appointed time or may not even list at all. They exploit the fact that it is done to know if the project is a serious or just another scam project.
If you have already find yourself using it before discovering the dangers or you have no other choice then make sure you try to use a more trustworthy CEX because some are shadier than others
Bare in mind that on the time that you would be dealing up with known exchange then you could somewhat assure that you would really be able to take back those funds if ever the listing is been canceled due to not to be able to hit up the right amount of deposit or whatever threshold that they had set out but its true that a certain project on being listed on having this kind of criteria is never been that good. Exchange platforms should really be listing out those potential projects because on this case, they might be able to list out some projects which might be scams or rugpulls because it is really just that easy to make out some manipulation and shows
that a certain project looks legit because its been listed.
Its true that its never been recommendable for newbies to join up but it would be all depending into you though because there are investors who are really that risks takers on something like this
because we know that the earlier you would be able to get in, the more profits that you could potentially be able to make out but of course the risks is higher which is something
that you would really be needing to deal with.