"grep searches the named input FILEs (or standard input if no files are named..." Important bit being "or standard input." Also, what an odd one-liner. What's

"grep searches the named input FILEs (or standard input if no files are named..." Important bit being "or standard input." Also, what an odd one-liner. What's the use case for this that makes it such a common command: file names and sizes for all files matching a pattern beneath the current subdirectory (and all subdirectories and files within subdirectories matching that same pattern)? Genuinely curious.