Your bankroll is NOT what you currently have deposited on the site.
Your bankroll is whatever amount of money you have set aside for playing poker with.
If you're willing to reload a certain amount, at a certain rate, you have a much larger bankroll than someone who wants to deposit one time and then grow it from there (or never deposit and build from $0).
Let's say you like to play 4 tournaments a week. And, you have $50 to deposit each week. You can play $10+$1 tournaments on that bankroll. If you only wanted to deposit once, you'd be limited to $1.00+$0.10 games. If you happen to go broke in all the tournaments, you just redeposit the next week and give it another shot.
You'll probably not lose all the games (hopefully not). Say you break even, the next week you'll be able to deposit another $50--if you want. Then you'll have $100 to play. You could move up in stakes. I would probably move up at a 50% rate. Meaning, you would move up as if your account was $75 not $100. In this case, you'd play $15+$1.5 games the second week. If you lose all of them, a deposit the week after allows you to give them a second shot. Losing again would bring you back to $10+1 games. You'd be able to keep taking shots up, as long as you are willing to keep depositing, keep winning, and feel like you can beat the games.
Or you could not deposit again, unless you lose, and keep moving up or playing until you went broke.
You have a lot of options, if you're willing to deposit. Since you have a much larger bankroll. If you deposit once, you need to be more conservative about moving up and the games you play because going broke means you're unable to play anymore.