Linux works very well with disc sizes of less than 1g. There are lots
of these older discs around and if you want to make a firewall or other
application which doesn't require lots of disc then these are excellent.
If you are planning to use a large server then a new disc is a must.
As I have said before older discs don't have the checks that modern
discs have. There are even modern 20g drives that require you to
lockout bad sectors.