If they're good (which is pretty fucking rare), they should be identifying issues and blocking and escalating them to people can fix it, taking pressure from above without passing it on to their workers, having a fair few of those useless meeting with other middle managers to share information and insights so people aren't working against each other or implementing significant change that will fuck up things their workers are doing, advocating for more staff if needed, persuading senior management not to do stupid shit, developing staff (including finding them jobs and making connections for them when they're reached the limits of their current role), etc.