If you're not gaming then what CPU speed does for you is speed up your work. A Celeron, for example, can do the same things an i5 can, they'll just take longer. Time, as they say, is money. If you don't mind a computer that's a bit slow to do things, then a Celeron is an option.
In games this isn't true. That's because game performance, frames per second, is very dependent on CPU speed. Dropping below a certain level makes the game unplayable. Dropping below a certain level in music production just means everything takes longer.
Personally, I can't stand doing anything on a slow computer. Those little waits for this and that all add up over time.