Compressing Video Files

Sorta new to mac... I have a bunch of videos that will start to take up a lot of space and I noticed that you can right click and "compress" the file. What exactly does that do and can i still watch the video if it is compressed? Also how much space does it save if any at all? Thanks

Mac OS X 10.6 Help: Compressing files and folders

Once you have compressed the file, you will not be able to view the movie. You will have to uncompress the movie file first, to view it.

To add to what has been said, I'm assuming your video files are in a format that is already compressed so any further compression would most likely worsen the video quality. If you are okay with that then you can further compress them but you might want to think about getting an external hard drive so that you can delete them off your internal drive.