I have yet to have a shop do anything on any of my cars. I haven’t done a whole lot though. My “big” projects include 2x clutches, 1x timing belt, intake manifold swap. I’ve done everything else from rewiring 15-20 wires to swap to a newer computer in my car, mounting and wiring gauges, mounting intercooler & making my own piping/mounting, etc. I havent had to tear into a motor yet or anything like that. I would probably do the bulk of that myself but for the machining / assembling I’d take it to a reputable shop because that is something I don’t have the knowledge/tools to do and wouldn’t trust myself “learning” on my own motor.
The main big reason I do all the work on my cars is because I enjoy it and it gives a lot of satisfaction knowing I did it myself. A CLOSEEEEE #2 is the saving on labor costs, which can be a LOT for more extensive lengthy projects.