The other thing you can do is run all of your footage through Handbrake to compress it a bit. Might not work if your source recording is already H.264, but if you're doing PC recording with any kind of lossless codec, it will smash the files down into something reasonable.
I save all my stuff. You never know when you might need it again. Most of it just goes to my file server.
I backup to internal SATA drives that I slide into an external drive sled. 3 or 4TB HDDs are fairly cheap. I also mirror those backup drives to CrashPlan as they don't delete anything.*
Since CrashPlan thinks the drive sled is a local drive it will backup everything on it, even when I swap it out with other drives. I've already uploaded 3.1TB of data to CrashPlan. It does take awhile.
I've had a backup drive go bad on me once and I lost an important computer image. If that computer every went belly up I don't have a way to restore it back to that configuration. That's why I keep two sets of backups.
*In most cases they don't but they will delete if you remove a folder from a backup set. All file associated with the folder go away.
If you can, save everything. If not, for some of my older videos I just saved a two reasonably high quality exports of the video: one normal and then one without the music track (just in case I need to re-upload in the future if I have any licensing issues).
I see it as get a external hard drive and fill it up but also when you import your video to edit save one or two B-Roll clips from it just in case then you can save those and determine if you want to save the footage your not using and so on.
Im a gamer and I play DayZ. If you do not know what DayZ is... basically you can go around for hours without anything happen... and then all of the sudden you will experience something crazy. I record everything into a folder called "temp" (short for temporary). When im done playing if nothing happened I delete it. If something did happen I drag it into a folder called "edit" (telling me to edit the footage). Hope this helped