It would be super handy for the Grenade Launcher to be able to shoot *up* more, on occasion. Aliens on rooftops (esp on Mid East maps, with those huge targets roof areas), and behind fences etc, currently get an easy ride, because you need considerable lateral displacement to make the angles work. Being able to switch to high register fire would just make them slightlier easier to deal with on occasion.
The same might apply to thrown grenades, presumably, and grenades from underbarrel launchers, if they eventually make an appearance, and any other weapon with an arced line of fire. It might also be useful for passing equipment, say tossing a medikit over a fence or onto a rooftop so a wounded trooper could be healed more quickly, rather than waiting for a medic type to run *around* the fence / get up onto the roof etc.
As a sidenote, I'd also like to see the GL get a small boost in range, like 5 squares or so. It wouldn't overpower the weapon, IMO, and would better differentiate the weapon from thrown grenades. Currently, it doesn't really have that much more reach than a thrown grenade, and real life GLs have a range of a couple of hundred metres, clear across pretty much any map.