The Windows updates are often important, typically patches for vulnerabilities that have been discovered in various components of the operating system.
As important are keeping web facing applications such as Java, and the flash player up to date. Past vulnerabilities in these sorts have items have usually been a factor when a machine becomes infested with malware. It can happen with machines that have all their software up to date, but is more rare, and usually then as a result of an infected web page or the user inviting the malware in. ("You must have this codec to view this movie. Download now?" is a typical sort of invite. Invariably the movie is promoted as a sex tape or wardrobe malfunction regarding some Hollywood starlet. The reality is even less appealing.)
What I'd do is set the security centre, in respect of window updates, to "notify me but don't download or install them". The second Tuesday of every month (called "Patch Tuesday) updates are released. Shortly afterward, you will be notified, by the presence of a little yellow shield in the system tray, and a balloon tip: Updates are ready for your computer (or similar.) You can then choose when to download them and install them, at a time you aren't using the bandwidth for anything else.
I've found that going to the Windows Update site (Internet Explorer only) is a lot quicker than letting them update via the automatic update feature. Don't know why.
I'd recommend
Secunia PSI as a status scanner for all installed software. It will periodically scan your system and let you know if there are out of date items installed, for which a patch is available. It defaults to doing this automatically, and scanning every 21 days, and starting with Windows. It can be configured to run on demand, however, and you can then run it manually when it suits you. (On install, then every 2 to 4 weeks would probably be a good idea.)