A pentest is more than just exploiting one host my friend...
My point is more along the lines of using Powershell to easily access network resources using the added features. Also you don't necessarily need to install it since it is required for certain server apps like Exchange 2010, and Windows Server 2008 has it as a built in feature (not to mention Server Core).
Plus, it's basically the same as running python and having the immediate interpreter at your fingertips, except it's PS rather than PY.
"Live as though you would die tomorrow, learn as though you would live forever."
CCNA, MCSA, MCTS, Sec+, Net+, Linux+, CEH