Withdrawal of winnings isn't just the issue because you can withdraw your winnings and then still put the money back in it again because maybe you actually didn't use the money well the way it's supposed to be used. There are so many cases that have resulted to gamblers getting all addicted because of the lack of will power to actually make that decision of yours withdrawing their funds and using it wisely.
No I still think that withdrawing your funds after winning is the best thing to do because I don't no if you have hold money on your betting site before, so that you will understand the temptation that's associated with it because immediately you have a lot of funds inside that's when you will be very tempted to gamble all the time, though I'm not saying that everybody are the same because I believe that there are people who has a lot of funds and still control themselves from gambling too much, however the best thing to do is that if someone is able to understand themselves they should no if keeping there money on the gambling site is okay for them or not because for me I would not hesitate to withdraw my wining from it.