both the angled down and non-angled hit people hanging on the edge, and angling it down doesn't give much more use for edgeguarding thanks to the auto-sweetspotting of brawl.
The only interesting thing that people don't already know about this is that the angled upwards fsmash does 1% more than normal, has more knockback (kills about 5% earlier without DI), and sends them more upward (by a very small factor), and angling it down does 1% less than normal, has less knockback (5% later without DI), and sends them more horizontally (again, a pretty negligible amount).
Sonic's main use of this would obviously be for angling it up to have a slightly better chance of hitting opponents approaching from the air. You can angle it while charging, or by holding up while csticking the fsmash.