Why create many partitions?
There are several reasons:
- System robustness. If you have /home on a separate partition from /, then a regualr user can't fill up the / filesystyem, making it unusable for the rest of the system.
- Backups. It makes it easier to back up entire partitions, and to back up on different schedules. For instance, you might only need to do weekly backups of the system partition, but nightly backups of the /home filesystem
- System installs. You can have the same /home filesystem mounted by several different system images. And you can delete and rebuild / with out doing a backup/restore of /home or /local
- Disk optimization. Not as much of an issue with todays fast drives, but it used to be common practice to put the system filesystem on the inside tracks of the disk to speed up access
- Using multiple drives. Before the common availability of large drives, it was common to have little room on the system drive. So a separate drive was used for /home.
- NFS. When sharing data across multiple systems, it is common to do it on a filesystem basis.
I typically create one for root, one for swap, and one for home. The advantage of this is that it allows you to leave your documents (also music, video, pictures, etc) untouched if you need to reinstall the OS. Because you can completely over write the OS partition (root) without touching the home partition, your files are safe and there is no need to perform the time consuming process of transferring them to another media and then back to your fresh machine. It makes reformatting/imaging much more elegant
Here is some more info on the benefits. Although its written about windows, the principle is the same.
Having /var and /tmp on separate partitions are also generally considered good ideas; that way, if a log file (for example; any temporary file) spins out of control, it will be stopped before filling the entire disk.