Saved links, and images.

It'll make any computer slow. You're cluttering it up with a lot of stuff, the computer has to search through.

One thing you can do is, you can transfer the information to a storage medium, such as a CD or DVD if there is a lot of it.

Images (jpgs in particular) can be rather small, and links are tiny. Sound files, though, are large.

If you save your stuff over to a CD or the like, then you are covered if your computer crashes (assuming that the CD is; if such things worry you, then burn 2 identical CDs and you'll always have a backup).

Thanks jespah.