For example you could use admin.domain.com to lead to the admin area.
But using a subdomain for every sub section is pointless, and it would require you to set up a new subdomain whenever you added a section.
There aren't really any advantages, no.
The major difference is that a subdomain can point to a complete separate physical machine, or some arbitrary folder inside your document root folder.
Just think of it like this: if your website is a building, does it make more sense to put the new section in a room inside the building, or to put it in a completely separate building?
It needs to have a page called index.html before that shows as a page without the file name.
It's all up to you. There's no right or wrong way. How you create the subdomain depends on your hosting company.
