The bandwidth/memory savings are the main reason one would use them over float, and that's a big one. Not sure if it's still the case but in the desktop GPU world texture filtering was once easier to come by with half float instead of full precision float textures.
I know less about mobile GPUs, but I understand bandwidth is if anything even more of an issue there.
Bandwidth is indeed even more of an issue on mobile and it will
almost certainly be the case that filtering will be more available
for half-float than float for the same reasons it was once "easier
to come by" on desktop.
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