Why automounting on startup? (These are just few reasons.Might be lot of other possibilities)
* the collection of wallpaper you using are placed in that partition
* Icons for launcher which is placed in that partition
* You want it to be available each time you boot
Why use gvfs-mount
Usually when talking about automounting on startup people would suggest user to add entries in /etc/fstab. The problem is that if we mount a partition from fstab, we need to have admin right to unmount/remount the partition. And another uncool thing is that if we automount using mount command & entries in fstab, anything that we delete from the partition will not go into trash instead it will be deleted from your harddisk as soon as you click delete. You wont find it in trash, believe me.
Automount using gvfs-mount is a totally opposite story. Any partition you mount using gvfs-mount command can be unmount/remount without administrative privilege. Besides that anything we delete will go to trash first. So if we accidently deleted something we can find it back & restore from trash.