Serious question on the above topic. The spaceship "Discovery" in "2001: A Space Odyssey," used a rotating area to simulate gravity of (seemingly) 1g throughout the flight to Saturn. Wouldn't that require the same expenditure of energy on the part of Discovery as simply propelling itself at 1g toward Saturn? The rotational force isn't "free," right?
The rotational force isn't free; one pays for it at the beginning by investing the necessary action-reaction energy expenditure to set the vessel turning.
Once begun, however, there is little to slow it or stop it. Minor changes in rotational velocity are manifested by the change of position of various masses, including human bodies, but in comparison to the mass of the ship, these are hardly noticeable.
Of course, any long-term development, such as the designation of a new storage area, would have to be offset by shifting other weights around to balance. Think of rebalancing the washer when it chokes on a load of towels.
Short term dynamic balancing can be effected by pumping liquids from one tank to another. And an aggressive dynamic balancing can be maintained by rotating a large mass at the center of gravity of the vessel.
The major problem with artificial gravity in space habitats is having "enough room to swing a cat". Space is normally at a premium in space. Some suggestions have been to rotate masses on long tethers to maintain artificial gravity. One familiar with our history and geography will note that we use an effective compromise; the Habitats go around a common axis of rotation, and are connected together with strong arms which contain our pipes, conduits, and transportation system.
Only time energy is 'free' is when liberals have a new pet boondoggle to foist...