Personally, I can say that I have more deposits, so I don't need to check my record if I'm doing fine because I would only be upset, lol.
Just as you have said, @OP, let's assume I have a $100 bankroll and I increase it to $500. That means I have made a profit of $400, right? What I will do is withdraw the $400 and only leave the $100 I initially started with. I don't have to wait until I have lost almost all the money up to $10.
If perhaps am not able to increase the $100 far more and I ended up to lose all of it just in one day, I will definitely leave and not repeat again through out that day but if I had allow all the $500 to site in my casino balance, I will definitely have the urge to keep trying luck and before you realize it, i must have already lose all the money, so it's better to save yourself of the temptation and withdraw your profit, leaving behind the amount you are willing to gambling off. I don't love to spend too much on gambling just in one day, $100 is even too much to waste just in a daily staking.