Not saying this in the interest of starting/continuing an argument, but unless the cost is going to be prohibitive I prefer to get any reasonable tests/cultures done before treating. Not an RI, but I had a snake come down with a typically mammalian parasite a few years back. The vet initially wanted to do a general treatment, but I decided to wait on the fecal to be done before treating. Had we waited till the general treatment failed to do the test it would have certainly been much worse (if not too late). Considering the amount of stress it puts on reptiles to go to the vet and get the meds in their system, I just personally prefer to get as good an idea as possible before treating to minimize the amount of times they have to go through that.

That being said, I do understand the logic behind doing a general treatment first, and there are upsides to both strategies. It's just down to the keeper to decide what works best for them.