Why should text files end with a newline?

Question

I assume everyone here is familiar with the adage that all text files should end with a newline. I\'ve known of this \"rule\" for years but I\'ve always wondered — why?

Answer 1

Imagine that the file is being processed while the file is still being generated by another process.

It might have to do with that? A flag that indicates that the file is ready to be processed.