How is `requestedAmount` different from max permitted amount?

[sebastiantf]

What exactly is the difference between SignatureTransferDetails::requestedAmount and TokenPermissions::amount?

If using a permit for less than the max amount, and the nonce will be used & invalidated, then whats the use of having the two different numbers? Aren't they the same at that point?

Essentially i'm trying to do this:

1. Get a single permit signature (not a batch transfer permit) from Alice for spending T tokens
2. Transfer X tokens directly from Alice to Bob
3. Transfer Y tokens directly from Alice to Charlie
4. X+Y = T