Fragmentation increases badly....some files take longer to access because of the compression ratios....and I think you may have to compress new files once they hit a certain limit, I'm not sure.
 
If you are talking about the disk compression that NT has built in, where you can compress files to save space or whatever, bad choice, because if you switch to FAT32, or reinstall Windows, you may have a problem accessing them....including using PartitionMagic.
 
Once when I did that, and tried to use PartitionMagic, it told me that I had compressed files and couldn't do that, so I uncompressed them, and then when I finished the PartitionMagic job, all of my files were ****ed.
 
Old File Name and Extension: oneandonly.wma
New ****ed File Name and Extension oneandon.ly and another appeared called oneandon (no extension)
 
It ruined everything.

The latest Partition Magic works just fine with NT compression...( had to add some free space to my c drive since the dvd rip proggie I was using didn't let me rip the audio to my D drive).....I haven't had a problem with it yet.

Sure it does, because I've done it before. But one time, it did screw up like that. I'm just warning him of all possibilities, so that we can't be blamed