It occurred to me that Lubomir Sedlacik wrote in gmane.os.netbsd.help:
> i think it's a waste of disk space.  for desktop use i recommend swap
> and one big partition to hold the whole file system.

Three things:

1. Putting everything in one big partition increases the risk of damaging your
   root partition during a system crash, thus making recovery more difficult. 
2. Having an mfs (or tmpfs) /tmp pays.
3. You may not want to have everything mounted with the same mount options.