wow ...now I'm surprised ... I have one of these things (but the simple ones u get @ a pharmacy), but I use 'em at all times in a club except when I'm djing.... This generally helps a lot 'cause u only hammer yer ears when u dj... but still U tend 2 lower and eq the monitors 4 a more balanced correctly leveled sound....
I realise this might b silly but My realisation was that if I had the plugs I tended 2 have the monitors LOUD (in fact I didn't even need 2 touch the monitors level fader 'cause most guys already play really loud), so the sound comes out distorted... plus what happens is U actually increase the SPL by decreasing the rms .... also like some1 posted U loose the high detail, which is good 'cause u spare yer ears, but it's quite bad 4 every1 else cause u tend 2 over compensate with the eq thru out yer set, so most punters will have over excessive Highs (I say over 'cause they generally r already excessive)....
So my conclusion is U really need a lot of self discipline and training 2 get used 2 them with out abusing...
On another tip I realise that most of the time I end up not using the plugs all that much 'cause there is always some 1 who wants 2 talk 2 ya about yer stuff, records, tracks, partyes, djing etc... and if u hav' em on U can hardly keep a conversation and after 2 hs u don't have a voice aswell...
Hit me back with yer thoughs/ experiences about this!!
Z