Personally, I grease fasteners (on bicycles) that are A. more delicate (like a cassette lock ring), B. two different metals (such as the rear derailleur with a steel bolt to an aluminum hanger), and C. areas where specific torque is important (like carbon fiber bars in an aluminum stem). Probably easier to list where I don't use grease...brake disc bolts and caliper mounting bolts (which have thread locker on them), water bottle cages, front derailleur hanger bolts, and brifte/shifter/brake lever bolts.