Not sure why you're asking this on the iPhoto forum, but here goes:
Your HD is, to all intents and purposes, full. You have the bare minimum of free space required to run the OS and apps and you need to make more space on the disk.
OS X needs about 10 gigs of hard drive space for normal OS operations - things like virtual memory, temporary files and so on. Without this space your Mac will slow down as the OS hunts for space on the disk, files will be fragmented, also slowing things down, apps will crash and the risk of data corruption - that is damage to your files, photos, music - increases exponentially.
You have 10 gigs at the moment. You do not want to let it get any lower.
Defraying or any other things will not free up space. What free up space is finding that is using the space and then - where possible - moving it off to another disk. There are no utilities that "erase crap" and you really, really should avoid any that claim to. What they regard as "crap" may well be your priceless data.
So get looking. One way to do this is to download an app like Grand Perspective
http://grandperspectiv.sourceforge.net/
It will give you a graphical representation of what is using your disk space and allow you to choose what to delete.
One very strong tip: do not delete anything whose purpose you do not understand. That's how you turn a computer into a paperweight.
