This isn't necessarily true. Your variance for multi-tabling may very well be less than your variance for single-tabling which means that your bankroll requirements need not always be larger.

Refer to my earlier post and the link below for an alternative take on playing multi-tables as a way to reduce variance.

http://www.cardplayer.com/magazine/article/14233

Yeah, I know why. I am not seriously advocating putting 50% of my roll on the table. What I was doing was posting at 2:35 in the morning after a long and frustrating day in real life. This seems to have led to me being even more incoherent than usual. I was also confusing myself by looking at the matter from an SnG viewpoint even though OP was clearly talking about cash games. I will now compound the problem by posting after 2 AM again having come off a 16-hour day.

What I was trying to do was challenge the analogy being drawn by Bacon that implies that playing ten tables for one hour has the same risk as playing 1 table for ten hours. This may be true, all things being equal but all things are almost never equal when you change the number of tables you are playing at. Most importantly, your win rate will almost certainly change. For the ADD-challenged minority, your win rate may actually go up as you add the first few tables, but eventually everyone will hit a point where adding another table will reduce your win rate. As your win rate declines, your bankroll requirement will tend to go up. Of this, I was, and still am, reasonably certain.

There is another aspect of risk that I was thinking about, but I am less sure how it affects bankroll guidelines. I was thinking about SnGs tho', not cash games. This applies when you have a comfort level - a value of roll which, if you fall below it, you will cease to play at the current stakes, and move down to lower stakes.

With cash games, if you buy into a number of tables at the same time, you can get out of all of them more or less at the time your roll drops below comfort level for your current stakes. IOW you can have more money on the table than the amount by which your roll exceeds the point at which you would drop down. However with SnGs, if you buy into a set of games all at the same time, your money is gone. You hope to win some back. You don't find out whether you drop below your comfort level until after you have already spent your money. To avoid falling below your comfort level, you must not put more money on tables than the difference between our roll and your comfort level. IOW, to play on the same number of tables and have the same dollar value comfort level, you must have a higher roll for SnGs than for cash, and your bankroll requirement tends to increase more with the number of games you play at one time.

I actually had trouble winning at NL10 and NL20 until I multitabled. NL50 is hard for me unless I have at least 7-9 FR tables going. Multitabling usually eliminates FPS and takes away 99% of tilt. Just don't have time to worry about bad beats at all, usually there's another hand coming up one second from then. Plus the long run comes faster. Plus having 8 tables of a easier level behind 2 tables of the level I'm learning increases confidence. And the wins from the easy level pad the downswings from the next.

I do try to keep more buyins like 30-40 if possible but only because downswings could reduce # of tables. I don't see more risk if someone can beat the level they are multi-tabling. It would only be more risky if they have trouble concentrating, or have bad tilt problems where one hand affects all other tables. If I played SNGs I would keep more BR.

The choice for many players is playing x-tables tables at their current limit or y-tables at their current limit, not x-tables at their current limit and y-tables at a lower limit.

Lucky