Boot - There's plenty of uses. The main thing I use it for is to aid in recovery. Many recovery techniques leave you lagging a bit before you can move again. This is bad. You can edge cancel to take care of this, however. Try to land near an edge and slide off - significantly less lag time to be punished.
Even with L-canceling, there's still a substantial amount of lag on both the links' dairs (just to mention a couple) which can be punished. I find myself using Ylink's dair a lot more if I know I can edge-cancel it if I miss, often jumping into another air move immediately (or run the hell away throwing things).
I'm surprised Phanna didn't show Samus' uses for it. Maybe because they're not as flashy/spamy, but they've saved me quite a bit. Samus' Screw attack is commonly used defensively against enemies that are a little too close or pressuring her shield. This can leave her lagging and vulnerable, at times so much so the opponent will get a free hit in. You can (fastfall) to an edge and get rid of the lag far quicker than your opponent typically will recover from the screw attack, often fast enough to get another hit in (usually bair) if you're lucky. On levels with platforms (specifically Yoshi's and FoD) this is a lot easier, but I've used it on Final D plenty.
There's a ton of other uses, hope this gives you a good idea to start with.