What is the difference between mounting in fstab and by mounting in file manager

..and what are the consequences of the different methods? I have been trying some things with the mounting of an sda2 partition. Mounting in fstab, not mounting in fstab but from the file manager. So far, if I am right, I learned that by mounting in fstab, a partition is mounted automatically at startup. But this mounted partition is not shown under 'devices' in the file manager, whereas the root partition and cdrom for example are shown. When you want to have it under devices in the sidebar, a partition should not be mounted in fstab but by clicking it in the file manager. Is that correct? But which way to go if you want both? Automatically mounted at startup AND being shown in the sidebar of file manager?