algent It's also because it depends on the aim of the permanent partition.
For example, an enterprise may use an image to install its servers and have the home directories on a NFS volume, so the server could be reinstalled without the user data & settings are touched. -> This permanent mount point would be /home.
Personally I have a few mount points for my NAS on /mnt/... backup, multimedia, public, ... I consider them as permanent although they are not since they are only available when my laptop is @ home and connected to the LAN.