I had an old Triumph Herald once which seemed to wear unevenly, but not necessarily on the same side. I was too mean to chuck away a half worn pad when I could see no practical reason to do so. If the braking was uneven or in any way affecting the car, then I would think differently. But I never found a problem with this.
If you're a commercial outfit and you only replace one side and the customer has an accident, even for a disconnected reason, then maybe you're for the high jump, in the same way as you have to put a lid on a take-away coffee in case the customer burns himself. But in practical terms I cannot see the problem.
Rob