What does it mean to paste a function around some lines of code? As in what're the manual steps you do because that's not possible today?

I assume auto-wrapping a copied function signature around a selecting block as if it was just parentheses or something. I don't think I ever needed that, but a variant of that might be useful for XML where wrapping something in a pair of tags is a common operation.

Mostly I would find this helpful during refactoring where it’s normal to move some code out in to a specific function. It would also be helpful for loops, if/else, validation, try/catch since you could copy the boilerplate and paste it over the code block in one move.

I don't know what exactly you mean by pasting a function around the selection, but you can paste selections, registers or even files at specific lines with some vim-fu. If it's generic enough you could write a function or even a keyboard shortcut if it's very simple.

I have set ",',(,[,{ in visual mode to cut the selection insert the pairs then paste it back as a very hacky solution, but it gets the job done. If you want something more advanced to add or change anything around the selection tpope has solved that with vim-surround[1].

[1]: https://github.com/tpope/vim-surround