I am basing my opinion on an admittedly small sample size of one booth, the eastbound Vernon-Jackson 7 train exit. The station agent has a permanent cover over the transaction window and cannot conduct commerce.

Since the tracks are between the platforms customers must exit the station, cross the intersection and use the westbound clerk for human transactions. The eastbound station agent is frequently out of the booth (on the street, in the bar?) or otherwise consumed with self-important tasks such as reading or napping, none of which are beneficial to the riding public.

Although I pass through this exit each afternoon I have never seen the station agent assisting any passenger in any way. There is no elevator for the disabled.

While station agents at other stations may be of marginally greater value it is clear that these are just make-work positions perpetuated by the TWU. If it was up to me these useless seat-warmers would all be made into full-service booth operators, re-purposed within the MTA, or released.