Correct! But knowing what’s what is still an advantage. When I see what is being installed in roofs nowadays, just so structural engineers earn enough, it makes me sick.
My roof is a simple gable roof and the rafters are basically just planks with straps in between. When I had to go into the roof at my best friend's house to check the ventilation of the drains, I saw right in the middle a glued laminated timber beam measuring 20 by 30 cm, from which only a few ceiling joists were hanging, beneath which there were even walls!
Yes, what do you have, a rafter or purlin roof? With the former, you don’t need that, with the latter it doesn’t have to be unreasonable. It also depends on the dimensions. I’ve never heard of deliberately oversizing trusses anywhere anyway...