my experience,
If you have $200 in onboard credit and go into the casino and charge $100 to your room and play with it and win, you will upload those winnings to your card or get chips that you turn in
you will now still have $100 in OBC but when you go to cash in winnings if you are lucky, you will get them in cash
if you upload the whole $200 at once and win, you still get to keep all your winnings, provided a single win doesn’t go over the taxable limit
not sure what happens with table games, but if you hit a slot jackpot over (it was $1200, but not sure what it will be) a set amount you will have to fill out a tax form there.
not sure if they will take out the taxes or not, do used to be lucky, I am not
if you are playing slots and your credit in the machine is getting up there, load it onto your card and then keep playing if you want