The post directly above perfectly captures the logic behind the "Please Wait" light.
The wait for the electromechanical RAT to do its thing can seem much longer than it actually is, and there are perceived long periods where there are no clicking sounds. Considering how many people don't read operating instructions or perhaps don't remember the portion dealing with the cancel function, it's easy to understand that service calls could ensue.
Not everyone has the mechanical inclinations to understand how the RAT works. Somehow they don't apply the same logic to the cancel operation as they do when they've stopped a cycle to add a forgotten item. Once the door is opened, you need to push the cycle button again to resume after the door has been closed and latched (also true on MAT models). The same applies to the cancel function but it's not exactly intuitive to push the cancel button again to tell the machine to continue the process of not doing something. Even the "Please Wait" light won't help if the door is unlatched too soon, but the logic behind it was to prevent the door from being opened in the first place.
Almost exclusively, the cancel button on my ISE Classic Supreme gets used when a toddler has played with the panel or someone has leaned against it. I'm getting into the practice of leaving the door unlatched to avoid this issue. With the KA latch design, the handle sticks out when lifted, and as a result when I had a KA I always latched the door. With the side-to-side latching action of the ISE, the look is much more discreet when the door is not latched. $250K well-spent by Emerson? I'm beginning to think so!