Transposing can help vocalists. It can also help instrumentalists play in keys that are easier for them, or they are used to. That's another use for capos.
Alternate tunings are good for making it possible or easier to play certain notes together that might be more difficult (or even not possible) to play in standard tuning. Examples:
Open G allows you to play major chords bay simply barring across all the strings on the same fret. This makes slide playing easier.
Drop D gives you 2 notes below the low E that normally wouldn't be available.
One of my personal favorite examples is Van Halen's 'Top Jimmy'. There's no way to get those notes as natural harmonics of the intro unless you retune to that open Dm7(no3rd) chord. And the rhythm guitar part uses that tuning for some standard chord voicings but in somewhat unusual sounding patterns.
So, it's essentially another way to be creative & give you options not normally accessible.
Hi Christoper,
You are just a GENIUS!
I tried searching for some info on the topic, and it wasn't really useful. You made it very clear and simple to understand. It's even better in text.
On top of it, it only makes us appreciate Eddie Van Halen a lot more. I keep seeing references to him on multiple answers here. Just ahead of his time.
Really appreciate the reply Christopher. Have a nice weekend.