I do not know what you like but I am an action type of poker player. For this reason I like to play at many tables at the same time. Although many tables can provide a lot of action it is still not enough for me. I like to play many different types of poker. And sometimes the high quantity of tables definitely decreases the quality of my play.
It is an important topic to discuss. If you love the game and play it for fun, it is okay to play at many tables and be always in action. However if you play poker for a living then you have to find the optimal number of tables first. Too few tables are not good because you are losing revenue. Too many tables either because you are missing out on some of the important action and you cannot concentrate on your best game.
Lately I have discovered another, maybe not so common mistake in my play. I tend to play many different types of poker at the same time. The variety includes NLH full ring, PLO full ring and short-handed, Stud full ring, PLO 8 or better and tournaments. If I play 5 NLH tables and 5 PLO tables it is ok and one game does not influence the other.
The problem comes when I play PLO and PLO 8 or better at the same time. The games look similar but the strengths of the hands are completely different. And when the action is fast because of the many tables, it is easy to make mistakes. For example an Ah7s8h9s is a very nice hand in PLO but a complete trash in PLO 8 or better. Or As2h3c4d looks great in PLO 8 or better but you would never play it in PLO. I have lost several times because of the windows changing so fast I misclicked and made a call with a mediocre hand. Of course you can separate your display, two sides/two games but you will be still confused a couple of times.
The same is true for tournaments vs. cash games. Here you will see a different kind of problem. Although the game is the same your strategy is totally different for a tournament and a cash game. In a cash game you can risk more, on a tournament you risk the whole event in every hand. Still, in a cash game you can wait for a long time to have great hands, but on a tournament you do not have hours to wait for monsters because you will lose your stack over time. Both problems have happened to me, because of the high amount of tables I had and I could not concentrate on the current action.