It would likely have a negligible benefit for composition, even if notating unassisted by any pitch aid.
Since the intervals (not frequencies though) between scales are consistent regardless of the pitch of the tonic, one could compose a piece using relative pitch that they believe to be in the key of C, when actually they are "hearing" it in Bb. Precise relative pitch ability has much more utility in composition, absolute pitch would have more advantage for performance (choral starting note, woodwind tuning, on-the-fly assessment of string fingering).
It would only be useful if for some reason you needed to compose and then perform a piece without a reference pitch.
Since the intervals (not frequencies though) between scales are consistent regardless of the pitch of the tonic, one could compose a piece using relative pitch that they believe to be in the key of C, when actually they are "hearing" it in Bb. Precise relative pitch ability has much more utility in composition, absolute pitch would have more advantage for performance (choral starting note, woodwind tuning, on-the-fly assessment of string fingering).
It would only be useful if for some reason you needed to compose and then perform a piece without a reference pitch.