Windows 7: Windows Defender - what does it really do?

And is it really of any value? I get updates every 2nd or 3rd day, sometimes every day which I am sure is for Defender files. I would like to eliminate this annoyance.

Windows Defender - Windows 7 features - Microsoft Windows

I have disabled Defender - I have other protection in place. Defender is just too much in my face all of the time. My other protection runs without needing to tell me about it all of time. I guess this attitude comes from being a SW developer/tester for so long that I don't have the time to continually (every 3rd or 4th day) reboot my machine and wait for this thing to do its update. We always used other protective measures.

This question is now moot.