How to measure frozen herbs, like dried or fresh

Dry rubs are one case that I can think of where dry is specifically necessary, so you can grind them up properly.

The main advantage to dry herbs is that they're available year round. When you're dealing with winter dishes, dry herbs would've been the norm to have used at that time.

If you are going to substitute, you'll need to add more (typically about 3x as much, as the dry is usually more concentrated), and you'll want to add it late in the cooking process, while dry herbs are usually added early.

One exception to the rule is bay leaves -- you'll still need to add them early, and you'll want to reduce the number.

The Cook's Thesaurus is a great resource for these types of conversion and substitutes. There conversions differ for each herb, but for rosemary, they list

1 tablespoon fresh = 1 teaspoon dried