Even without checking a bag you still have to wait in line with at the terminal ticketing counter to get a boarding pass. Other airlines let you get a bording pass online.
The line to wait in is the same as those waiting to check bags. This extra step is a thinly veiled rouse to get you confused and pay $25 dollars for a checked bag.
It is unnecessary and easily circumvented.
The stated reason for the inspection is to verify if your bag will fit under a seat. Other airlines don't impose this needless time wasting step.
I will not be flying United again if another airline is available for my destination.