Avoid compressing the files if you need more space. You won't feel it at first, but over time (as superfetch starts to work its magic), you'll get random freezes, especially if you've got hundreds of large chunks files like videos or ISO files. I used to do the same, and the random freezes kept me stumped for quite a while (I even changed my videocard thinking it was going bad, since the freezes happen while playing games). Turns out it was the 128 gigs of compressed Ps2 ISOs that was making my PC freeze.
The freezes are not exclusive to when you're accessing the files. Sometimes Windows will try to index the folder/files on its own and BAM - unresponsive PC. You can move the mouse but everything else is hung (This happened to me while I was browsing porn and I heard the wife opening the front door. God bless the PC's physical power button.)
And worse, there are times when compressed drives get messed, resulting in some of the boot files being compressed as well, which means you won't be able to boot windows (will give you an error to the tune of a corrupted or modified boot record).
Ideally, you should just get an external drive and move the files that you don't really need on a daily basis (e.g. movies, old backups, etc) on it. It's more practical in terms of backups as well - if your laptop craps out, it's gonna be hard to get your files out of its hard disk. If you had them on an external drive, just stick it in another pc and you're good to go.
