Does Slimming World make sense?

A lot of my colleagues are doing Slimming World until they get bored of it, and the amount they talk about it is another question (“Do you know how many sins that packet of crisps is?” “I don’t care, I’m not tracking them.”) But one thing makes no sense to me, perhaps someone can clear it up.

There’s a concept of ‘free’ food, and you can eat as much of it as you like and that’s fine. So in theory, could you eat 5000 calories worth of this free food every day and still lose weight?