Honestly, how did you pick your exercise to begin with? Is it too easy or too hard? If it's too easy then it's probably not the right exercise. It's actually hard to determine what's ideal or not. I think it would depend on what you're doing and if you're putting your energy fully into it, what your goals are for doing the exercise etc etc. ultimately you have to listen to your body.
I know that the exercise I am doing for myself is ideal to me because my body feels a lot better afterwards compared to a bad exercise where I feel unfulfilled