Accepted answer
To be exact about it, what the label says and what the trial protocols permitted are different documents, and the difference is instructive: protocols generally allowed a step to be delayed or reversed for intolerance, and a substantial minority of participants used that provision.
Missing a dose by three days on a weekly schedule takes the trough down by less than a factor of 1.35, which is well inside the variation you would see between two on-time weeks. Missing it by five or more days is where the label instructions start to differ between agents, and the reason is how close the next scheduled dose is rather than any mechanistic threshold.
Mechanically, extending the interval and reducing the dose are not equivalent manoeuvres. Reducing the dose lowers the whole concentration-time curve proportionally. Extending the interval lowers the average but deepens the trough, and for a compound whose effect on appetite tracks concentration, a deep trough is felt.
SURMOUNT-4 is the withdrawal trial to read on the maintenance question: after an open-label lead-in, randomised withdrawal produced substantial regain in the placebo arm while continued treatment produced continued loss. It is the cleanest available answer to "what happens if I stop".
One qualification — this is protocol arithmetic and reported practice, not a recommendation. The compounds in question are not approved for human use when supplied for research.
If you take one thing from this: dose rate drives tolerability, dose level drives exposure, and they are separate levers.