if you're a winning player more hands per hour is an obvious advantage to multiple tables. not paying close attention to how people are playing on that individual day and just relying on hud stats could be a disadvantage.
One of the biggest advantages of multi-tabling, other than to leverage a positive win rate, is the experience acceleration and shortening of your learning curve because you can see so many more hands per hour. online poker already plays so much faster than the live game, then add multi-tabling and this is why the internet has produced so many phenomenal players...they compact years of play into months.
Playing multitable can give you much more action/hands per hour and respectively more money if you are winning player at your level. I have tried up to 3 tables and it is too much for me. Two i can handle but it affects my ability to monitor other people gameplay and sometimes i need to take decisions very quickly compared with just one table. For me if you want to play at more than 2 (maybe 3 for some people) tables you will need HUD software so that you can take necessary decisions very fast.
I will add that on microstakes by playing 1-2 tables sometimes you will make more mistakes than playing 6-8. Seems strange but sometimes if you are too much focused on action, you make too many notes on villains and try exploit their tendencies you can make your game harder and too contrived (? I don't know correct word. But I hope you understand what I mean). This is not how it should work . Make your game simpler, just make volume and probably it will be more effectively for your poker skills and bbs per hour.
I agree with some comments above. Playing more hands gets you ore experience, lessens the likelihood of playing too loose, and you're more likely to grind out a win if you're a winning player. Multiple tables allows you to hedge your bets and ride out the variance more quickly on a losing streak. However, you can overcommit yourself and start playing poorly so you need to learn what your limit is. I prefer being able to concentrate on 2-3 tables maximum, any more and I start to lose my edge.
I used to multi-table (4 to 8 tables) in order to see more hands per hour. Now I just play one Zoom table. I see as many hands but can concentrate on a select group of the same players and never get into a time-compressed situation where I have to make decisions on four (or more) different tables at the exact same time.