End to end gets weird. I was asked to look at an admin page, nobody could figure out why it was 30s. Literally the first thing I tried got it under 4 and the second down to three. It was pulling the same list of rows twice, applying two filters and then looking at the intersection. I changed the signature to send the list as input instead of the query constraints. Then I changed them to avoid the intersect.

If you would have asked me to bet on which one would have had the bigger impact I would have split the difference.

My second favorite was similar. Two functions making a call instead of sharing the answer. Profiler said 10% cumulative. I removed half. Instead of 5% I got 20%. Which just demonstrates how much data a profiler cannot show you.