I did a little testing of this process because I had never paid attention to it before. This mfpmp.exe does not start when WMP starts, but it does start when playing most music or video files. Purchased music downloads and videos, even MP3 files, have a "Media Usage Rights" setting which you can see in WMP by right-clicking a file in the playlist and selecting Properties. Even though there are no restrictions on MP3 files, and some others, WMP still lists the Usage Rights, "This file is not protected". For any such file, mfpmp.exe gets loaded and apparently does all the work of playback. At least, when I played a 720p WMV video file, the CPU usage for mfpmp.exe hovers around 13%.
Using MPC Home Cinema, I can play the same video and it does not launch mfpmp.exe. It also uses less CPU bandwidth -- around 10%.
Bottom line, you should not disable or kill the mfpmp.exe process when running WMP. That would stop it from being able to play most files. You could, however, use another player such as MPC-HC or VLC as your primary playback software.