That is true -- but easy movement among levels is not something on which to skimp. It is fundamental to players' ability to choose their level of risk (and commensurate reward), and they should not have to spend much time slogging through familiar precincts. A bit of seeing familiar sights can be pleasant, letting them relish the signs of victories past before restocking (if you engage in that dynamic) in effect undoes much of their work. The situation should be a very, very far cry, though, from having to "clear a level and defeat the boss" (or find the hidden key to the next level) as in a video game before proceeding to whatever new challenges they may choose.
Here's another note related to mobility, brought to mind by reference in another thread to the Temple of Elemental Evil. As I recall, about 60% of rooms therein were occupied by monsters. That is basically the opposite of how a traditional D&D dungeon should be: The 1E DMG recommends that 60% should be empty -- at least in terms of monsters, treasures, tricks and traps. (In OD&D, the figure is about 56%, "in the same ballpark").
If players are to do more than just wander about kicking in doors and getting into fights, then they need space through which to maneuver with some freedom. They need "empty" chambers to facilitate reconnaissance, and also to enable evasion of pursuit.
In the latter regard, branching and turning (to block lines of sight) corridors are also most helpful.
