Why does it matter what the subject is?

I see a lot of questions asking "what is the subject"? (This, for example.)

Why does it matter, practically, what the subject is? How does knowing the subject give more information than just knowing what the sentence means?

In the linked example,

And up here in the corner is me.

My understanding is that this sentence is being said by a person and that person is saying that they are up in a corner.

What if the subject is "here in the corner"? What would that tell me?

What if the subject is "me"? What would that tell me?

Solution 1:

It is of no use at all to users of a language as users. You can use a language your entire life without knowing what a Subject is, just like you can live your entire life without knowing anything about metabolism.

But teachers trying to explain to a learner why a particular expression is wrong or why a particular expression requires a different form, or programmers trying to develop algorithms for translating from one language to another with a very different syntax, need a 'metalanguage' for talking about how language works. Subject is a basic term in that metalanguage; and the question you linked is a question about linguistic theory dealing with an 'edge case' where the standard terminology seems to obscure understanding instead of promoting it.