Yes, quotes are tools, but are they truly useful? A good speaker can express their one thoughts without quotes. Using quotes is like showing your own inadequacy. You need someone else's words to validate your argument. Using quotes makes it seem as if your own word is not good enough for people to listen too.

Well you could use a quote to explain something to someone who couldn't understand otherwise.

However, if you were to modify the words you used it's possible to make what you're getting across clearer than the quote. The quote would have to the _most_ clear way of sending the message possible for this to not work. Which would be ridiculous, in any event.

Quotes are always more static than your own words.

People also tend to pay attention more about the subject in mind when they know the quote is from someone famous.

That discredits you. One should aim to be quoted than to quote others.

Okay, listen. Someone you've never met before walks up wearing a tattered trenchcoat and stinking of booze, and he's trying to convince you the world is actually flat. But you know very well it's round, because that's what your mother taught you.

He then quotes Albert Einstein, Sir Isaac Newton and the current Dalai Llama all stating that the world is round, and providing extremely convincing arguments.
You look into this, and find that the world's greatest minds all agree on this fact.

It's called credibility. He could sit there for hours and try and tell you the world is flat but you wouldn't give a damn. His word means nothing to you.