Example:

Get me a drink please? That’s a general request, not detailed.

I could get you water, pepsi, tea, whatelse? maybe herbs?

Now you can be a bit specific with “I need a drink, IF you can get me water I’d like it, ELSE (if not) I do not want anything else”.

This specifically tells the person what to request for and the action to take when water is available, and also another action if he/she doesn’t find, “return with cash”