Maybe OP means "application to a concrete example" to help the reader understand. If a paper is presenting a theorm, seeing it applied to an example could actually help.
Yup. I don't mean "here's how you can use my theorem to build a bridge", I mean "here's an instantiation used to prove a more tangible result". Bonus points if multiple such results fall out of the general theorem. That's good evidence to me that generality is actually accomplishing something.
Because it's an expository paper, not a reference manual. Applications help communicate and create understanding.