In practice
The last group does the most useful work. It makes exclusions explicit instead of leaving them implied.
MoSCoW categorizes work rather than ranking it. Every item in “must” is equally required, so the method breaks when that list gets too long. Teams often cap the must-have group to stop everything entering it.
Why it matters for product builders
A written “will not” is one of the strongest guards against scope creep. It is much harder to quietly reverse than an unspoken assumption.