Re: "allowed to play" - when I am playing bass, I try to take as many chances as I can within a given context and, in the spirit of Mr. Lesh (a huge inspiration to me, along with Mr. Casady), I try to push the boundaries of whatever musical framework I am associated with.
On more than one occasion, I've been told this, or something very similar: "The songs we are playing were / are popular for a reason. It is not our responsibility to re-invent our individual parts on the fly as we see fit. Learn your part and play it like the recording."
Needless to say, I tend to lose interest in those projects fairly quickly...
If Phil would have received that admonishment and behaved as instructed, we would not be having this lively discussion.