WMV File Size??? Data vs DVD???

I have just imported a few videos from my digital video camera and have
noticed some considerable file sizes. One video I imported came in at 5.24
GB. When I take that file and prepare it as DVD the file size becomes only
844MB. Is one of these what I see referred to as a data file and then the
other is a DVD file??? They are both file type .WMV. What's the
difference?? Once I have my DVD is there any need to keep that large data
file. Should I copy the large file to a disc? Etc. Etc. Any insight as to
what I'm seeing and doing here would be welcome.

Thanks,

bj