So what's the use of tx id's at all then? I mean practically speaking, since they're mutable? I'm thinking of an analogy here but I can't. It's like a git commi

So what's the use of tx id's at all then? I mean practically speaking, since they're mutable? I'm thinking of an analogy here but I can't. It's like a git commit hash, but you're "allowed" to append some whitespace to the end of a file so you can keep mutating the hash but it's the "same" commit. I don't really see a use for tx ids if they keep the spec as-is then or am I missing something?