Those wheel bearings are designed to run in preload just like pinion bearings of a differential. They are properly set up when they take a certain torque to sustain rotation (about 15in-lbs if I recall). They should not be loose and they are a major event to disassemble. Proper reassembly requires crushing a crush sleeve spacer until proper preload drag is accomplished.
I'd wait till there was a problem. New bearings pale in comparison of cost to the value of labor, in doing the job.
Bosch Master, ASE Master, L1
33 years MB technician