If they get the rosin too hot when pressing they can mess up the terpenoid profile, which effects the flavor. If it's done properly you should end up with most of the terpenes in tact. Also, if the grower added sulfur to solve a powdery mildew issue or something like that, it can end up concentrated in the extract. I like to let the terpenes polymerize before doing the rosin process. I just end up with a better product than live resin.