What are the major roles and responsibilities of a staff sergeant?

For me, it would be mentoring and guiding the E-5s to ensure they are mentoring and guiding the soldiers, and be prepared to fill in for your platoon sgt.

SSG(P) (Join to see) have you looked at the DA PAM 600-25 for NCO professional development? It used to have the skills, knowledge, and abilities by MOS and grade for career progression in that MOS.

I think the big thing is the different spans of control. As a PSG you are managing 4 Squad Leaders and mentoring a Platoon Leader to accomplish Platoon tasks and missions. As a Squad Leader you are managing 8-12 individuals to achieve Squad tasks and missions. As a SFC or even a Senior SSG, you aren't leading individuals all the time, you are leading teams.

As a Staff Sergeant and Sergeant First Class you'll start spending more time above the Company level. Bringing your line experience to the BN S3 shop running things like land management, training ammunition, QTB, schools, orders, battle tracking, taskings, etc. you'll work in closer proximity to the Commander and CSM which has a range of opportunities and challenges.

Great responses from the O's here. As an NCO you improve your jobs skills, trying to become not only the trainer but the expert in your field at the next level. Same for leadership, SSG normal have squads so you are talking serious counseling to subordinates. Now you dig into duty rosters, troop care and management. The list goes on, everything you were doing as an E5 has to be done at the E6 level with broader horizons.