The answer is simple and at the same time complicated as fawk. Many people agree that the more tasks you have, the bigger the cpu consumption. But this kind of thing applies to hundreds, maybe thousands of tasks, far from what someone would use in a common plugin.
To make a good example, in my server, when saving user information in database I use a player specific task, because I don't need it do execute at the same time for everyone and it gives me the power to set frequency depending on player.
I don't use looping tasks that execute on all users because I don't need them, for setting things like models, hud info I use forwards because they're more reliable and useful.
The only example of looping task that executes on all players I can give are the server chat advertisements.