I can’t see that much downside to using blue Loctite on many fasteners — stem, seatpost, brake mounts, etc. I’m not sure it’s necessary for most of those fasteners, assuming that they have been properly torqued, but by the same token I can’t see any harm, either.

Where would I insist on it? Rotor bolts, chainring bolts, and crank arm pinch bolts are a few places that come to mind.