This definitely used to be a feature - "See the map of the current level" - and I think it should be reimplemented. It's a source of learn-from-your-errors information for less seasoned players as to what they might have done wrong.
Yup, there was also where I learnt about the less obvious secret doors that weren't in an empty corridor. Also, adds to the despair of the player in SMC or DH knowing that they were only room away from the exit. ;)