Rumengh
Legend
Platinum Level
Depends on the Player and the stakes i guess. Its about Variance. The better you are compared to your opponents the less variance you will face because of the edge you have over them.
As a general rule of thumb you want to have a minimum of 20-30 buyins for your limit in NL cash wich would be 3-5% of youre roll. If you are a regular at 200NL online and by whatever reason decide to start at 10NL again, i can see people doing it with 10 buyins, thus 10% of the overall bankroll, but even for someone who crushes a limit thats a pretty aggresive bankrollmanagement, and it has to be expected that variance will crush you some of the time.
I guess 25-30 buy ins is optimal level for cash-games for recreational players, regulars have more buyins bankroll management because they dont want to go broke.
It is actually the other way around. If you dont think you can beat a level play with a deeper Bankroll. If you are a recreational that learns the game start with a 50 buyins BR. If you know for certain you will crush a level Yolo it with 5 buyins. Expect in both cases to go broke
If you are not a winning player, its not even possible to have a bankroll, you can only have a budget. And in that situation I dont think, it makes sense to set up general rules or guidelines. For some people it might be good to deposit 50BI, like you suggest, and let that be the money, they have set aside for poker for the foreseeable future.
Im completely in your side here but I am also assuming that whoever even thinks about BR management and reads/ writes in Forums has the will to get better at the game. So for someone that learns poker I would not suggest to deposit 20bi. They will go broke in both cases but depending on how serious your approach to the game is you might atleast have the chance to improve before busting the entire roll. Variance is huge, even over stretches of 50k hands, so if you are a slightly loosing player a bigger bankroll atleast gives you time to work on it.