Multi-Site Strategy

I would greatly appreciate opinions on the use of the following Multi-Site network structure to support a client environment.

Here is a domain name based structure I envision. Remember, this is one Multi-Site network.

Network Admin Account
bob.com —————-> Live site that public sees and interacts with
clientqa.bob.com —————> Quality Assurance site for designer use
clienttest.bob.com ————–> Test site for designer use

Of course the Network Admin Account manages installing and activating both plugins and themes. I see some advantages from a plugin management perspective.

What do you think? Is this practical/useful?

Thanks,

Jerry