One of the amazing things about heaving to is the sudden quiet and calm (in reasonable conditions)... luffing the main could be noisy and cause extra wear and tear.
However it is about balance, as has been mentioned. In our experience the main is quieted but not necessarily centered but there are plenty of variables here.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)