Someone explained to me that I could increase the surface area of my herbs significantly when grinding them in a mortar with a bit of salt. It is indeed quite easy to grind them down to a powder. I do have the impression though that my sauces get more bitter when using powdered oregano. Is there any basis to this? Am I just using to much oregano given its increased "aromatising efficiency"? Or am I indeed releasing some substance that would otherwise be locked in the leaves?
By grinding it, you are also increasing the surface are of the herb when it reaches the tongue, and you are exposing the raw/inner (bitter) flavors of the herb to the mouth. When cooking with it "un-ground", the cooking process extracts just the oils from the herb, and leaves the leaf in tact which does not taste unpleasant to the senses.
I would certainly use less of a ground herb, but my preference would be to leave it in it's natural dried state, and if you want more taste just increase the quantity. The only exception I have for this is when making rubs, where the fat of the meat (or oil for a bread dip) typically complements the bitter flavor of the ground herb.