The Microsoft AU Daemon is a small piece of software that periodically checks Microsoft's servers to see if there are updates to Microsoft Office. Given that Microsoft continues to release security and other patches for Office, it is probably a good idea to leave it running (or at least remember to check manually if you disable it).
It's impact on your system should be pretty close to 0 -- it's been running on every Mac I've ever used in this century and I've never had a problem
With that said, if you'd like to disable it...
1) Open System Preferences
2) Select Accounts
3) Select Log-In Items
4) Select Microsoft AU Daemon
5) Click the "-" icon to remove it (or just hit delete)
But again, there is no real reason to do so.