While the majority of patches tend to install without causing any adverse impact to the rest of your machine, occasionally a patch creates conflicts or introduces more flaws than it fixes. In those cases, it is nice that Microsoft includes a means for uninstalling the patch and restoring your system to its former glory.
However, once you have installed a patch and enough time has gone by for you to determine that the patch seems to be functioning according to plan and that there was no negative impact to your system, you probably don't need the uninstall data taking up space on your drive anymore.
You might not even realize the files are there. The patch uninstall data is stored in hidden folders under the main Windows folder. If you click on Tools - Folder Options and select the View tab, you can click on the radio button next to Show hidden files and folders to reveal the secret data. Each patch has its own uninstall folder.
Assuming your computer is running fine and you don't foresee suddenly needing to uninstall a patch for some reason, you can feel free to simply delete any or all of the patch uninstall folders to reclaim the hard drive space.
The patches will still appear under Add or Remove Programs however unless you remove them through other methods such as editing the Registry.
Tony Bradley is a consultant and writer with a focus on network security, antivirus and incident response. He is the About.com Guide for Internet / Network Security (http://netsecurity.about.com), providing a broad range of information security tips, advice, reviews and information. Tony also contributes frequently to other industry publications. For a complete list of his freelance contributions you can visit Essential Computer Security (http://www.tonybradley.com).