this is actually how I gig mostly
As the singer in 2 bands, I like the whole mix so I can make sure my voice sits in the right place, so I come out the headphone socket
Both bands have everything in the pa, so I get a great sound
I did a bass only gig last week (U2 Tribute) and we only had time for a line check, I got a kind of mix in my IEMs but not what I wanted.
The out front sound was ace, just not enough time to sort the IEM mix properly (and there's no way I was going to take them out)