I would imagine most company commanders have never had an XO. I was an XO for about three months while the old CO was preparing to leave, and I was the incoming CO. In my tree company commands (and one detachment command) I never had an Exec, but if I did I would expect the XO to basically shadow the CO, provide coverage when and where the CO wasn't available such planning conferences, YTB/YTC briefings and the like, and probably to take responsibility for some of the unit programs like UPL, some inventories, tracking whatever the CO identifies as priorities for the unit.

There are undoubtedly other things unique to the unit, but I would start by just sitting with the CO and asking what he/she could use a hand with.

Never had one when I was a Company CO. Heck, my first company command I didn't even have a 1SG. And when I was XO, I was practically CO in every respect except actual paragraph and line number.

Recently, I volunteered to become the XO of my company, as the position has been vacant for some time. Also, I figured it would be a good way to distinguish myself from the other Warrant Officers, who are all senior to me in experience.