All modern disk brake systems are "constant contact" - i.e. the pads don't actually retract any distance from the rotor. Various tests of power absorbtion or increased fuel consumption show that constant contact pads have no meaningful effect, but the constant contact quickens brake response to pedal movement, and simplifies the design.
In the case of 124s and 201s, of which most models share the same rear brake hardware, the parking brake is completely separate from the service disk brake. The parking brake is a shoe type with shoes inside the disk hat section that extend when the parking brake lever is pulled. This design is also shared with the '65 to '82 Corvette disk brake system, but most modern cars have a mechanical piston actuator that pushes the piston on the floating caliper to act as a parking brake. The 201/124 (and vintage Corvettes) use a fixed caliper design with floating pistons on each side and mechanical actuation is not practical. The front 124/210 brakes are of the floating caliper design, which is the most common type on modern cars.
I've found that over time the parking brake shoes glaze and loose effectiveness and the cure is to drag the parking brake a few times to slow or stop the car. This will break the glaze. Keep the button depressed so you can release it instantly if necessary.
The front wheels turn will little effort, but when you turn a rear wheel you are also turning the differential and transmission guts, so the rears will exhibit a lot more drag torque.