The advantage IMO is in the wind. If it isn't windy, I wouldn't want the extra weight. I find that I don't want an 10lb electric. I'd rather have it 12 lbs in the wind.
If you watch Troy Newman fly his Ys powered Pinnacle in the wind (as he fly's quite fast) he doesn't get bumped around. It cuts through the air. Not that his plane is heavy, because I doubt it is. But the slow flight of the electrics tend to get bumped around IMO.
Add a little ballast and you cut through the bumps a little better.
Of course once I go down from a 22x12 to a smaller prop I may think different. Just haven't done it yet.

I have seen people with glow that have a very very large tank and fill it completely on windy days. Landing with over a half tank still.
Same concept really.

C