I find they offer an extra position as the bars are still round towards the outside and only flatten off heading towards the stem. I don't use the tops much at all, but when I need another position when suffering on hills, they seem fine to me.
I've noticed that the pros seem to either ride on the drops, obviously, or their hands are very close to the hoods, or are on the hood themselves. There seems to be a more normal round section to the bars at the point where the STI aero levers are.
I route the gear and brake cables along the front of the bars to give an oval feel to them. I find that more comfortable when gripping a round tube. I also use non padded bar tape wrapped as tightly as I can get it so it almost feels like I have uncovered handlebars (Which would suit if it didn't look pants). I find it more comfortable to hold them like that and have no issue with fatigue in the hands.
But as with all things like that, it's horses for courses and I doubt if my way would suit many others.