Optimization is a weird thing to grasp at first
One of the biggest shocks I see from citizen developers who move their app onto a server is that their (calc-heavy) reports run like sludge. I'd say it's a near-universal for those who are new.
My very first attempt at a big report was like this. I had a lot of summary fields, unstored calcs, and plenty other obstacles. Because I didn't use Let statements, my calculations were a Great Dismal Swamp of tangled nestedness. Instead of using utility layouts for certain steps, I used methods that guaranteed cross-script interference. It was bad, but it's also representative of every report a non-developer produces in Filemaker.
I don't find the need for this sort of optimization strange in itself. If the cost of being able to create an integrated business environment this quickly is that you've got to employ a few different techniques that aren't covered extensively in the training manuals, then things are pretty good.
I've learned a lot of tricks along the way. Moving the results of unstored calc fields into regular number fields. Running 'on server' scripts that basically populate the report ahead of time. Stuff like that.
What has helped you in making faster reports?