IMHO, nobody's given the basic answer for running -12db with todays recorders. Back in the day you were recording in 16bit technology. Today even the lowest end flash recorders use 24bit technology. Back in the day we ran hot to make sure we got the full dynamic range on our recordings. However, the resolution provided with 24bit means you don't any lose dynamic range if you record with alot of headroom and then bump the levels in post.
The second concern to running with lots of headroom was decreasing the SNR and amplifying the noise floor in post. However, noise specs have also improved on gear and most people find that, unless you record nature sounds, for the type of recording most around here do, the noise floor never becomes an issue. I don't always run at -12db, but I have no concern bumping my levels that much in post (or even more) as long as I've recorded in a 24bit format.