A single word can hold a large amount of meaning, but to the brain that single word uses the same "storage" and any other word.
So by having many complex words a person can think more "efficiently".
This is why many fields have jargon - the jargon helps the thinking process, by essentially acting like file compression - you compress an entire concept into a single word, and you can now think about some big complicated thing by using a single word.
This is also why language have so MANY words. English has something like half a million of them. Yet it would be totally possible to replace the vast majority of them with simpler, but more, words.
But doing so has drawbacks to thinking ability.