You shouldn't be pulling up media files with your media tool. Do that and you'll blow away the actual audio and video.
If you want to get rid of your render files, set your Media Tool to show only Precomputes. This will pull up all your render files, and any graphics you imported, as well as your Avid generated titles. If you still have the files you imported (say Photoshop graphics) and you plan on backing them up, then delete all your precomputes. When you have to bring the show back online just load the backups of your imported files and do a Batch Import. Avid generated titles can simply be rerendered in Avid.
If you aren't backing up your imported graphics, be careful when you delete the precomputes. You might want to make a bin of all your imported graphics, select them all, choose to Show Media Relatives (which will highlight their related Precomputes in the Media Tool), then Reverse Selection in your Media Tool (so you're selecting everything except the imported graphics), then delete.
If you run into problems, let us know. Deleting precomputes is a great way to regain some harddrive space and backup your projects.