Optional but Smart! The .Net Framework should be considered like minor service packs to your system. As such, it is always a safe practice to set a Windows Restore Point before installing them. It usually takes about 30 seconds to create one.
Here are instructions if you are not familiar on the procedure.
A Restore Point allows for the rolling back of system files, registry keys, installed programs, etc., to a previous state in the event of system malfunction or failure.