Do you mean like replacing lower roller guide wheel(s) in a 6’ pit?
I’ve always utilized a second mechanic as there really is no other way to get this replacement done by ones self safely unless there is a 6’ ladder at your disposal. I suppose any work where the unit has to be lowered to the point where a safe and adequate exit point cannot be provided would require a second mechanic to run the car.
Hope that example addresses your question.