A procedure can be invoked for various values of the argument. All rights reserved. What is good and what is bad, is obviously a matter of style. I see no reason to forbid such a notation, it is compact and simple, but I agree that it might mislead the beginners. Unfortunately it shows once more, that the semantic status of Maple needs some clarifications.
Maple provides several useful programming tools, but lacks a methodology.
Maple is wonderful, I am not trying to suggest that the policy of the creators was wrong. I, and my adolescent children use it for some daily chores, but its semantics is too rigid, this is not an evolving system any more. For example, it can be used to define the base case of a recursively defined function without explicitly programming a test. Then naive users would be protected from themselves, but users who want to could still define function on points. But what is the distinction between x and Pi.