Asking what a person means when they use a word is not pointless - it's the only way to understand what they believe about the world. If you say "sound" and precisely define it as "auditory perceptions by a human", I then understand what you mean when you say "a tree falls in the forest and makes no sound". If you don't define "sound", then I might think you mean "a tree falling in the forest creates no vibrations in the air".

In contrast, using the word "vibrations" or "fred" instead of "sound" doesn't change the physical behavior of the air. That's why disputing definitions is pointless.