Hey,
I use both back in the stone and power trust when I can, and there is why :
BitS is fun to use, way more than hero spin, so that's why i picked it up in the first place. It's a good vertical recovery, but a terrible horizontal recovery.
It's not too hard to edge guard, but if you miss your edge guard you get spiked, so most people don't risk it.
You can use it to edge guard characters that don't sweet spot very well with their upB (cloud...), just upB from the stage and aim for the ledge. If you are a bit late, it may ledge trump so it's still good.
It's also really good when used after a Dair gimp, because you need to recover vertically, and it forces the opponant to delay his recovery (if he can) or he may gets spiked.
If you hit someone on a platform but don't land on the platfom, you can jab lock him in some cases.
Last but not least, it's an amazing combo breaker. The move gives you invincibility on the beginning of the move (frame 4 i believe, but not sure). If your opponant read it, you may get punished for it, but not as hard as if you failed marth's upB or something like that. I think it's the only way mii sword can escape a combo ?
Now power trust :
I started to use it because I liked chakram way way more than the other sideBs, but using BitS without any other recovery is a terrible idea imo. I tried power trust, and unlike Falcon's downB it's a decent horizontal recovery. Power trust->BitS makes you recover really fast, and don't let your opponant the time to set up and edge guard. Of course, if you eat a down smash at hight%, you are ****ed, but the rest of the time you should be fine. Basically, if you could have recovered with one of the sideBs, you can also recover with powertrust->BitS or powertrust->jump->BitS faster and safer.
Something that most people don't know is that it's a good kill move. Not a strong as strong as Fsmash, but it sends the opponant with a nice horizontal angle, so it can set up an edge guard. You can use it to punish landing, a whiffed attack, or to catch your opponant offguard after you zoned him with chakrams for a while.
Since it deals between 8 to 13%, it will clank or go through pretty much all (if not all) projectiles.
It's also a nice way to mix up your landing if not used to often.