This depends entirely on the distribution of the other categories. Look at this like optimizing a program. If you do a profile and one function takes up 80% of

This depends entirely on the distribution of the other categories. Look at this like optimizing a program. If you do a profile and one function takes up 80% of the profile and everything else is a tiny fraction, sure, focus on that hot spot. But if you have many many slow functions and none is a clear hotspot, they all need attention, even the 2.5% one.