While reading the documentation of Frappe Framework, I came across this:
Multi Tenant
Bench supports multi-tenancy out of the box. It means you can spin up multiple instances of apps with separate databases on the same codebase. It also supports port-based multitenancy where you can set up multiple bench environments for different versions of apps.
I don’t really understand this. Can someone help me to shed some light on it?
You can host multiple sites over one single bench. Or even, manage multiple benches with different sites over each bench. This capabilities lets you to save a lot of resources.
Imagine deploy erpnext (or any frappe app) just one time that can be used for many businesses (one site for each client). Things like maintenance, updates, etc … become easier.
If you use frappe or erpnext just for your own business is less useful 
Take a look here:
Hope this helps.