You should partition a disk (or disks) according to your needs. In my experience on Intel, Alpha, and Sparc platforms, for a fairly loaded system (feature-wise), doing a fair amount of tasks (as a desktop system at home, or as an Internet server at work), I have found the following approximation of space works pretty effectively for determining a partition size.
Given: A given disk of X Mb/Gb (eg. 2 Gb) (Or, more than one disk with a combined total of X Mb/Gb) Calculate: (swap) about double main RAM (eg. 64 Mb system gets 128 Mb swap) / (root) about 10% of available (eg. 200 Mb) /home about 20% of available (eg. 400 Mb) /usr any remaining space (eg. 1272 Mb) /var (optional -- see below) /boot (optional -- see below) /archive (optional -- see below)