Question

What is the main value of knowing the general meaning of a word's prefix or suffix?

Answer 1

Because context clues can help you find what a word means, so if you know what the suffix or prefix is, then you can use that to help find what the meaning of the word is.

Answer 2

A suffix is at the end of a word whereas a prefix is at the start of a word for example quietly=ly is the suffix
disapprove=dis is the prefix