For you, it sounds like you are more comfortable not playing several so stick with what you're doing.
I'd say it depends on the player, their experience, familiarity with the player pool at their level etc.
With more experience, the more they have been in certain situations and they find decision making easier. They can play more mechanically without having to think long and hard very often as they've been in similar spots before.
They might not perform quite as well at each individual table with the more tables they add. Still, it can be the right move for them if it results in more total profit at the end.
Easy example - A player typically makes 6bb and hour playing one table in a cash game. They make 4bb an hour on each table if they play 2 because they can't give all their attention to just one table. 4x2=8bb an hour so they make more money playing 2 and it's better for them than playing one. If the same player made 3bb an hour from each table when playing 3 tables then that is better still, 3x3= 9bb an hour. Less per table, but more overall per hour. If they then try to play 4 tables at the same time and only make 1 bb an hour at each one then they're down to making 4 an hour which would be worse for them than all the other options.
The same principle applies in tournaments, and scales up no matter how many tables we're talking about. They might lose some of their edge in a specific tournament but because they're playing more of them at once, it can be beneficial. It can also harm them. Everyone will have their own sweet spot of how many tables they can manage.
I don't know your experience, but beginner players should always start with very few tables, preferably just one, and only slowly add them. One day they might be able to handle 8, 12, 16 tables etc.
