Like to save LOTS of die-cut files, visit dropbox. It's a cloud location and you get 2GB free, initially. The site tells you how you can get more space too.
Even if you save your files to an external location (external hard drive and/or cloud), you should still save the files to a SD card or flash drive once or twice a month. Also, the less files on your local hard drive, especially images, photos, and videos, the better. Saving a ton of files like the ones I mentioned on your local hard drive will slow down your computer. If you have your files on a local hard drive folder, click on the properties to see how much space you've used for that folder alone. It adds up for sure.
The dropbox would be great for saving files that are too big to email (like the videos you want to share, but don't want to put on YouTube). You can upload the files to dropbox and provide a link to your recipient(s). The other good thing is being able to access the files when you're away from home from any computer with an Internet connection. Imagine accessing your files while at a crafting event. You wouldn't have to worry about forgetting the files at home.
After cleaning off tons of files like I mentioned above, use a "Disk Defragmenter" process on your PC (Windows 7) and a "Disk Cleanup" so that your files can be stored in a way that will make your PC faster (if you don't have windows 7, do a search such as "Disk Defragmenter for (your OS name)".
It's easy to keep your hard drive clean, but it's really easy to forget to do backups until we lose our files (been there done that years ago and hope to never have to go through that again).