To clarify, turning this on would make it so YOU have to hit headshots only or it wont do damage, this obviously wont affect other players when they shoot at you. For most people, Deathmatch is warmup for ranked and it can be annoying to try to go for 1 taps but you end up getting a kill via a chest shot on a low health enemy. Let each player choose if they want their shots to only do damage on headshots at the start of the round, thanks rito.

Edit: theres a reason headshot only death match exists in csgo and there are hundreds of pros and youtubers that agree is training is beneficial