Both backlapping and spin grinding take away the relief angle. Backlapping takes away less, provided it is done correctly. I actually adjust and backlap reel mowers. For people whose mowers have never seen the spin grinder, and the relief angle is intact, a light backlapping is all it takes to restore the edge. I hate seeing shops sell spin grinding only and the reel adjusted for zero contact. 99% of the mower shops here do that. They will even take a reel that only needs a touch up backlap and spin grind the shiz out of it without reestablishing the relief angle. That only works on golf courses where the mechanic can spin grind every week and there is a budget to replace the reels often. Grind up the reel on a McLane or Tru-Cut and the homeowner is out around $500 in parts and labor to fix it.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738