I agree that the updates to .net framework are important if you have it installed however, correct me if I'm wrong, you are questioning whether or not installing .net framework is necessary. The answer to that lies in the programs that you install. As an example I once had software for a phone I had that allowed me to backup my phone, transfer pics to/from the phone, and even use it as a modem. That software required .net framework to run because it was probably programed, at least in part, in the .net programming language. It's kind of like having to have java or flashing player installed in that if you use websites that are programmed in either you will need them installed for the sites to work correctly. Microsoft likes to push the platform on you by default assuming that you need it and that I disagree with.
On a fresh install of a retail copy without anything on it you can try going without it and if you get an error from installing a program that requires it then install it. The program could be programed automatically install it. On an OAM installation some of the programs installed by the manufacturer might require it. My thoughts are if it is installed, leave it installed and update it because you might break something by uninstalling it. On a system provided by your employer you will definitely want to leave it.