Without hyphens, what would you make of the following sentences?
1. I saw a man-eating shark.
2. At the conference were 40-odd men and women.
3. Ancient history tells us about gift-bearing Greeks.
4. The college had to limit all-night discussions in the dorms.
Without those hyphens, you would have seen a male person eating a shark. You could very well see a man eating a serving of shark, but eating a shark gives you an entirely different picture.
You may have already attended a conference or two with 40 weird people, but the sentence above tells you there were approximately 40 people there. We do not know if they were all odd.
Gift-bearing Greeks is quite different than a gift bearing Greeks. That would be the Trojan horse.
Finally, the college is not limiting every discussion that takes place in the dorms at night, only discussions that last all night.
When you have one or more words that modify the noun that follows them, use a hyphen between those words that serve as adjectives if without the hyphens the meaning could be misconstrued. However, when the adjectives follow the noun, do not use hyphens. Therefore, you’d have celebrities who are hard to please or hard-to-please celebrities. Your choice.
Again, I don’t make up these rules; I just teach them.