I didn't use it personally - had a Navigator for that! He would announce "Off intercom - Consol count" at which point the rest of the crew would try and distract him so he would lose his place. Pictures of scantily clad women seemed to work best.
This was on the Victor which had pretty poor Nav kit. Occaisionally we would use it in anger but some of the older crustier Navs would do Consol fixes for nostalgia. Well, that's what they said. Personally I suspected it was because they hadn't worked out how to use the new-fangled Omega!