I don't know why it says that I removed the review request from @dr-orlovsky. Obviously, I want you to review this :) .

There might be some discussion here since dr-orlovsky previously had (perhaps intentionally?) schnorr::PublicKey by value instead of reference.
I think we should only pass by value when you give up ownership and I see no reason to do it here. And passing by reference when you temporarily relinquish ownership. I know it's tricky when things are Copy, but that's how it's currently implemented for the rest of the address APIs.

As an extereme, I don't think passing an [0u8; 100000] by value makes sense if we just want to access it's elements without any ownership.

To the best of my knowledge, Copy types should be passed by value and it should be the job of the compiler to figure out whether using a pointer internally is better. If it doesn't do that, I'd consider it a compiler bug.

I'd agree with making exception for Option<&Large> as I don't expect the compiler to be able to also do null optimization.

If you have some resources that indicate something else I'd be happy to learn.

By asking on rust-lang discord I am getting mixed responses. From https://stackoverflow.com/questions/38065331/should-i-borrow-or-copy-my-small-data-types, it also looks like it is opinion-based.

All of secp API is full of references for types that are Copy, so is rust-bitcoin.

There is another argument that references is that they are consistent with other APIs. Maybe I will to write a benchmark

My benchmarks say that it does not matter. They are very close in performance and within error of measurement to say if it really matters or not. However semantically, it makes sense to not consume the data because none of the underlying methods require references.

I would 100% support this provided we have underlying APIs that require passing by value. What do you think?

Created a new issue to get new input. People might miss this in the taproot PRs

In the interest of moving things forward (even though I disagree), I have made this pass by value.

Based on your last comment on #708, I don't care whether it's by reference anymore but let's not turn this into refactoring ping-pong. :)

Sorry for the delay. Fixed the nits