Well, their are a few different types of trichomes on Marijuana.
The trichomes located on the fan leaves you are referring to contain a very faint amount of THC (almost 0.00%).
IMO there only use is as nature uses it. For producing energy that the plant can use as it sees fit.
Don't cut them off......
I don't know the science of any of this..... but I do know that i topped off and snipped a few branches from a couple plants during vegging (maybe week 5 or 6) and after drying them I got pretty high smoking just the leaves.
I had to smoke a couple bowls, and the high was very heavy and tired... nevertheless there was def THC present. This turned out to be true from plants that turned out to be male AND female.
You should read up about ganja history, cultivation, etc. A lot of questions you may have could be answered with some E-books downloads, or maybe some videos. Determining peek ripeness will have a lot to do with the shape, and color of these glands.