[ubuntu-za] ARE .DEB FILES NECESSARY?

[vincent]

A possibly silly question.

Are the .Deb files, kept in /cache/archives necessary to re-install programs 
downloaded, should there be a mishap, or are these just used in the initial 
download process?

I have seen in the lists, that it's suggested using apt-get clean to remove 
these files in order to free up space.

Very Happy Holiday Wishes To Everyone - May The Coming Year See Ubuntu Grow 
Fantastically!
Vincent