The big advantage is of course that it is relatively anonymous, apart from the KYC. You can deposit as much money as you want, there is no one to check or view a transaction and possibly put it on pause as banks often like to do. And it also goes very fast, you can gamble fairly quickly on the site after an upgrade. And for a payout it is of course exactly the same story. Anonymity could also be a disadvantage if you have problems with a casino.
Unfortunately, this is currently only true for small amounts. Theoretically, you can use any amount, but I'm sure that most casinos will ask for KYC (at least if you win and try to make a withdrawal) so you should always be prepared for wasting time on this procedure plus being able to pass KYC - if you are under 18 or gambling is prohibited in your country, then you need to have a fake identity in advance.