Personally I find this very irritating bloatware.

I resolve to shrink my winsxs folder down from 6GB to something reasonable. Its not at all clear to me whats in there and how much space it takes as this directory is peppered with links which are probably not taking up this space. Its still causing me trouble however. I keep getting out of space errors.

Over here http://blogs.technet.com/askcore/archive/2008/09/17/what-is-the-winsxs-directory-in-windows-2008-and-windows-vista-and-why-is-it-so-large.aspx I found an explanation. I dont like it much especially the tone of it which appears to be saying 'buy big disks or else' in this except:-

"So yes, the WinSXS folder is very large, and it will continue to grow as the OS ages. I hope that this clears up some of the questions about why that is, and what you can do about it. Note that the Windows servicing structure and the layout of the store is subject to change."

How to shrink or reduce the size of the Windows Vista Winsxs folder

"The only way to safely reduce the size of the WinSxS folder is to reduce the set of possible actions that the system can take – the easiest way to do that is to remove the packages that installed the components in the first place. This can be done by uninstalling superseded versions of packages that are on your system. Service Pack 1 contains a binary called VSP1CLN.EXE, a tool that will make the Service Pack package permanent (not removable) on your system, and remove the RTM versions of all superseded components. This can only be done because by making the Service Pack permanent we can guarantee that we won’t ever need the RTM versions."

So I ran it: -

Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation.  All rights reserved.

C:\Users\me>vsp1cln
This operation will make  Windows Vista Service Pack 1 permanent on this computer.
Upon completion you will not be able to remove Windows Vista Service Pack 1 from this system.

Would you like to continue? (Y/N): y
Performing Windows Vista Service Pack 1 Disk Clean-up...
Windows Vista Service Pack 1 Disk Clean-up completed.