I think "pointless as a means of exercise" perhaps overstates it a bit. I agree you're not going to see much benefits in terms of cardiovascular fitness, but every bit of activity figures into one's energy balance. You often hear that even small little movements throughout the day (non exercise activity thermogenesis) can be the difference between maintaining weight homeostasis or having a few pounds a year creep into your life. Prioritizing walking seems like a good hedge against this if you're not blessed with NEAT.