I reckon you're right. I remember one time when my own carrier had a "supervisor" auditing his route, following him around with a clipboard and presumably taking down times in an effort to see if the route could be lengthened or some such nonsense. What really got me about it was that the neighborhood has not changed in 50+ years. The same number of homes on the same sized lots with the same mailbox locations. So why the time-motion study? My carrier told me later on that these "supervisors" were just positions created to promote folks based on quotas. The poor carrier busts his butt every day while they promote these yo-yos to follow them around.
The helper did not volunteer to carry the bag.
He also had a stop watch with him,and was timing every move the letter carrier made. The purpose of this was to find ways to get the carrier to work more efficiently so they could demand he deliver more mail in fewer hours. They try to get you to do stuff like walk across yards and step over hedges. When you first start at the post office,it's not unusual for one of these birdbrains to tell you,"Here is 10 hours worth of mail. I want you back in 8 hours." They expect a replacement to be able to handle a route as quickly as the regular mailman,despite not knowing all the "shortcuts". As you can probably guess,this didn't work too well with me. I'd come in after 8 hours and ask them what they wanted me to do with the other 2 hours worth of mail. This is the kind of crap that gets people to do stupid stuff like throw away K-Mart and other advertising circulars in a attemp to pleae their supervisor so they don't get fired.
None of the above applies to anybody who isn't white and/or hetrosexual,though. The only non-white carrier I ever saw get fired was a Philapino shop steward who got caught stealing government checks and trying to use them to frame a white woman carrier who wouldn't join the union. Even then they kept him on the payroll all the way through his trial and up to his sentencing. Hell,union dues even paid his way to the convention.