what's a sysadmin doing messing with the desktops and laptops? Generally does not fall under a pure sys admin's role of responsibilities.
In any case, there are cases where compression can actually speed up application/file opens. In particular, files can sometime be accessed quicker if it a file that lends itself to compression (ie: test files and the like that obtain high compression ratios). It can be quicker because of the need for less disk activity to read the file (smaller size on the disk).
However, it is generally not advisable to compress a whole drive..
Looks like files are locked. Try to boot in WinPE Live CD or something and re-apply clearing the compression streams from files. But sorry can't dig in it. If your admin decided to save space why do you want to decompress data? In fact NTFS compression worth having it even on already compressed data such as 7-zip archives. Try to compress something with archiver, make a copy of created archive and apply NTFS compression to it. Notice that in most cases data would fit cluster size resulting in no excess of unfilled clusters.