I think the answer also depends on the lift. I realize the OP was asking about deads, but when I do my widowmaker squats I figure that as long as I'm standing there holding the weight it doesn't matter how many breaths I have to take between reps at the end, as it's not really resting.
When I do my 5/3/1 deadlift set on week 3, I find that I can do the 5 and 3 sets with just enough pause between reps to make sure my back is still properly arched before each lift. However, on the max set I find that if I wait 5-10 seconds I can get one more rep in than if I just do them flat out, and since I'm usually only doing 2-3 of them that extra rep seems really important.
I do the deads in my garage, which has a natural slope towards the open door. Consequently I made some plywood pads that have a small raised lip on the downhill side. This way I am not dropping the weights on raw concrete each time, and they naturally roll forward just a little between reps without heading straight out the door and into my neighbor's driveway
As the other posters have said, I'm all in favor of whatever makes you stronger. If you're waiting a consistent amount of time between reps, you can compare your lifts in one session to those in another, even if you cannot necessarily compare them to what you could do with no rest at all.