Dont know if youve seen this thread on a very similar theme..
http://www.volvoforums.org.uk/showthread.php?t=108059
I think its well worth applying the handbrake when rolling at a slow speed to allow some friction and perhaps remove any rust buildup on the inside of the drum, when you think about it the inner 'drum' brakes are unlike say a car that might only have a drum brake on the rear where the shoes are actually used for braking. On a S60/V70 this would never get any friction between the shoes and drum if you only used it when stationary (as im sure most people do).
I could imagine there could possibly be a fair build up of rust on the inner drum surface. Certainly the cold and damp conditions would all add to this - only my theory has anyone else found similar ?