Think twice before you add more tables. If you don't have to think about any decisions you make (or, more correctly put, if thinking about them for a few more seconds doesn't make them better) then it's fine to add more tables. But I'm starting to lean towards massive multitabling being -EV for many players. At the very least myself. Since April 1st and my pro-poker experiment started, I played 10 tables virtually every session, for a total win-rate of 3bb/100, which is respectable but not monstrously good. And reviewing some of my decisions I think I could have beaten it for at least twice that if I hadn't been so busy clicking. The most sizeable "mistakes" take place postflop when meta-game situations/noticing certain stats or notes in time could have allowed to size my bets differently or take different lines but it shines through preflop too. I end up folding too much in spots where I could have gone for a 3-bet bluff or a squeeze bluff because I see "trash" and check the fold box. I sometimes fail to notice that there's a shortstack in the hand. Etc, etc. These are clearly situations where I know better, but miss key information in the heat of the moment. I believe these kinds of mistakes easily add up to $6 every 100 hands and so I could have played 5 tables instead of 10 if that means that I get rid of those mistakes.
Playing fewer tables for a higher win-rate, besides the fact that it may be +EV overall, also has the added benefit (again, speaking for myself) that I better notice new things and learn more while playing, and of course playing with a higher win-rate drastically reduces downswings so I have less to stress about.
