File Locking

I have a bit of a problem wrapping my head around some of it.

All examples I see, have you use an exclusive file lock when writing.

And a shared file lock when reading.

What happens if I don't use a shared file lock if I'm only reading a file?

That was a hard one. For your next question, ask what the difference between a thread and a process is and we can all be in high school again.