Using a monitor profile as an RGB editing space is one of the more retarded things one can do in color management. Monitors tend to have fairly small color gamuts, and change constantly with use, so using a monitor profile for editing is extremely pointless.
But selecting your current monitor profile (generated from colorimetric measurements of your monitor) to tell Photoshop the characteristics the display device you are using is absolutely critical, or Photoshop won't know how to display colors on your monitor properly. If you don't do this, all the time and effort spent profiling your monitor is wasted.
Regarding RGB working/editing spaces, ProPhoto is prefered, but Adobe RGB is fine for images that fall completely within its smaller color gamut. But that has nothing to do with your monitor profile.