There are a number of scenes from TOS where the Enterprise does not bank in order to turn, so its usage is inconsistent throughout the TV series.

One theory I've heard, though it seems more conjecture than based in anything from the ST universe, indicated that banking the ship for a turn would decrease the power required by the inertial dampeners and artificial gravity in order to keep the crew unaffected by the turn. In other words, in a banked turn, much more of the inertial force is along the vertical axis, which would keep it in line with the gravity plating in the ship's decks, requiring less effort from inertial dampers.

There are a number of scenes from TOS where the Enterprise does not bank in order to turn, so its usage is inconsistent throughout the TV series.

One theory I've heard, though it seems more conjecture than based in anything from the ST universe, indicated that banking the ship for a turn would decrease the power required by the inertial dampeners and artificial gravity in order to keep the crew unaffected by the turn. In other words, in a banked turn, much more of the inertial force is along the vertical axis, which would keep it in line with the gravity plating in the ship's decks, requiring less effort from inertial dampeners.

There are a number of scenes from TOS where the Enterprise does not bank in order to turn, so it's usage is inconsistent throughout the TV series.

One theory I've heard, though it seems more conjecture than based in anything from the ST universe, indicated that banking the ship for a turn would decrease the power required by the inertial dampers and artificial gravity in order to keep the crew unaffected by the turn. In other words, in a banked turn, much more of the inertial force is along the vertical axis, which would keep it in line with the gravity plating in the ship's decks, requiring less effort from inertial dampers.

There are a number of scenes from TOS where the Enterprise does not bank in order to turn, so its usage is inconsistent throughout the TV series.

One theory I've heard, though it seems more conjecture than based in anything from the ST universe, indicated that banking the ship for a turn would decrease the power required by the inertial dampeners and artificial gravity in order to keep the crew unaffected by the turn. In other words, in a banked turn, much more of the inertial force is along the vertical axis, which would keep it in line with the gravity plating in the ship's decks, requiring less effort from inertial dampers.