As someone who's done a bit of home perfumery (but not nearly as much as others), I've used and smelled natural ambrette (essential) oil. My experience with it is that It's got a nice light smell, though a little nutty, like sunflower seeds minus the salt or something. It's got more of a light vegetal quality, rather than a heavy animalic smell. And there's a slight sweetness to it. I can imagine that a synthetic form of ambrette might enhance the sweetness and general muskiness. For perfumers, you have to use a light touch with this oil, or it'll dominate your blend. And supposedly too much can give it a stuffy "old lady" smell, though I never used that much!
I had Chanel Egoiste for a while way back when, which has ambrette seed as a base note. I thought that's what gave Egoiste its sweetness. However, having later smelled natural ambrette oil and the way it smells in a finished blend, my opinion is that the sweetness, almost fruity/honey sweetness in Egoiste comes more from the rose, coriander and vanilla. Of course, you have rosewood as a topnote, which adds a dry cherry (and yes, woody) type of scent.