The main usage of hyphens are in clarification. This can involve joining a prefix to a noun (anti-tank, counter-offer) or linking compound adjectives together (well-received, well-rounded, lesser-known). In the former, they are always necessary because the prefix is meaningless if not connected to its respective noun. In the latter case, there is an often-overlooked rule that should be followed. Notice how in my last sentence I used a hyphen before rule? I could have also written "There is a rule that is often overlooked...". This should show you how the rule works: if the compound adjective comes before its subject should be hyphenated for clarity, but if it comes after, then it shouldn't be. I'll give you some more examples below:
She is a well-read scholar. She is a scholar who is well read.
This is his warmly-remembered poem. This his poem that is warmly remembered.
The whole idea behind hyphenation is that it links words together that otherwise might be misconstrued.
If you wrote "This is his warmly remembered poem." It would look as if you were incorrectly using an adverb (warmly) as an adjective instead of using it in conjunction with -remembered as a compound adjective.