I kinda started with one idea and ended with another, I think my 2nd idea was more accurate. I personally use the 2nd one indirectly I don't really have a "bankroll" per se but I have told myself I will never let myself get below 6 months expenses and if I get to the point where the stakes I'm playing make it likely I could lose enough to go below that I will move down in stakes.
For almost anyone, especially people where the stakes are determined by your capital and not your ability as a player, the larger the poker bankroll the more money you will make. You can afford to play in bigger games (even if it's only when the games are good), you can afford to take more thinner edges, and just in general the more money you have the more money you will make. For these people, I think you should be "paying yourself" the bare minimum. I think you need to start with x months of expenses put away, I prefer 6 others may prefer as few as 3 months while others may even want to put away a year+, but that's your life roll. Every month take another month's expenses (including estimate for alcohol/entertainment I'm not just talking about essentials) out of your poker bankroll. If you are really crushing and want to reward yourself with a semi-large purchase do that out of your poker bankroll. But in general the best investment you can make with your money is your poker bankroll, so I would tend to maximize that. Once you get to the point where your poker bankroll is sufficiently large for the stakes you play and you have no aspirations to move up, you can start treating the poker bankroll as a poker+non-ordinary spending money roll. Spending money is an investment just like poker is, just an investment in your happiness. Maybe you want to go on a vacation, maybe you want a big-screen tv. Just judge how it will affect your spending+poker roll and make the decision from there.
Obviously this isn't the only way to approach things, but I think in general it's better if you're treating poker as a business. If you have a full-time job paying expenses it's a bit different but still similar, you just don't have to have as much saved for expenses since you have a close to guaranteed paycheck coming to pay for that. If the paycheck more than covers expenses you can use some of your paycheck to go into the poker bankroll (or poker+fun spending roll) and if it doesn't quite cut it but you're making money from poker you can put aside a smaller amount than a full-time pro would each month.