It's up to you. If you're building your roll to move up, you obviously can't cash out all your winnings. But given that, it depends on how you want to balance growing your roll vs setting money aside for RL purposes.

If you're not looking to move up, you have even more flexibility. For instance, you can withdraw $X whenever your roll reaches $2X, $3X or whatever other number you choose as long as you leave yourself a playable rill.