When you play several tables simultaneously you will experience greater swings in your bankroll than if you were playing only at one table. You play a lot more hands per hour, and some times you can either loose or win at all tables at the same time.
When you play multiple tables your edge of skill will decrease, by not giving you full attention to one table. However, there are three reasons why good players that are focused normally will benefit from playing at more tables at the same time. When you play a few tables your bankroll swings will increase, but by adding even more tables you actually decrease your bankroll swings. Secondly, playing at one table will test the patience of many players and you can lose your focus. Finally, your total win-rate will be higher per hour.
For semi-professional players, it is important to choose those blind limit where their win ratio is highest, without exceeding the limit their bankroll is suited for. As an example a player with a $ 500 bankroll should not play higher than $ 0.50- $ 1 No-Limit Hold'em at four tables simultaneously. The bankroll should always be equal to 500 times the big bet.
Many players lack information on their successes at higher limits. Therefore you should play at least 200 hours at one limits before you know your skill at that limit. Another thing to remember is that the higher the stakes are the better the competition usually is.
Normally, players play better poker when they play at the same limit at all simultaneous tables (for instance, four $ 0.50- $ 1).