The common failure
Many companies build a monthly deck, gather functions in one room and call the result S&OP. The meeting can be perfectly run while the business still makes disconnected decisions the other 29 days.
What S&OP should really do
The useful part is the decision system behind the meeting: one demand view, one supply view, explicit constraints, inventory choices, scenarios, decision rights and a route from monthly trade-offs into daily S&OE.
The test
A simple test is to remove the meeting from the calendar. If the process disappears, there was never much of a process.
Where value appears
Good S&OP reduces surprise. It does not eliminate volatility; it makes the consequences visible earlier and forces the organisation to choose deliberately.
The useful part is the decision system behind the meeting: one demand view, one supply view, explicit constraints, inventory choices, scenarios, decision rights and a route from monthly trade-offs into daily S&OE.