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.