The frequency of wearing a harness largely depends on your dog's lifestyle and the specific activities they partake in. For dogs involved in dog sports or dog training, wearing a harness is a regular part of their routine. On the other hand, pets that are mostly indoors and participate in minimal physical activity might only require a harness during their walks or for a special outdoor dog show.
However, one must remember that any dog gear should not be left on for an extended period as it may cause discomfort or even result in sores. As a rule of thumb, remove the harness when the dog is resting or left unattended.