When breaching a room or ufo held by aliens, it would be nice to be able to toss a grenade in through a window or open door without having to stand in front of it. To have a solider to the left or right of the door throw a grenade around a corner. Right now you can really only throw one straight in. I guess there is the possibility that being able to toss a grenade around a corner would be too powerful and not in the sprite of putting your units in harms way. However, since it is being tossed around the corner the accuracy can be lowered.
When I first started playing, I didn't really use grenades at all. Now I have been making a effort to use them more. Breaching a room where you know (or believe you know) contains aliens always stands out as a time for grenades, but I always find it hard to get the grenades in. The balance could be a problem, but I think the idea is good enough for some discussion