In garrison, the duties are very simliar. HCAs (and subsquently, HSOs) are normally utilised by the local CBG to do the Med Plans for their exercises. Other than that...
In the Res F, HCA / HSOs can occupy the CO, DCO, Adjutant, Med Coy Comd, Amb Coy Comd, Platoon Commanders and Platoon 2IC...