I think big bankroll saves you from loosing. I mean if you are betting small amounts then if you have the right strategy and a bigger bankroll to sustain a longer betting time then for some reason I think mirtangle will work at some point and if you are luvky and you bet big you can recover all your loses. I think it's a matter of luck still. Without luck you will be a gonner.
A big bankroll is generally something that is much bigger than your starting bet, and can sustain if you use martingale, etc.
For example, if you only bet 1 bit at a time, 100 bits is a "big bankroll" as you'd have to bet 100 times to lose your bankroll. However, if you combined this with martingale, you'd probably need a bigger bankroll than 100 bits as the amount you need to bet multiplies fast.