I am sure they're optional, but as others have said, they are there to curb cravings and ultimately stop you from falling off the wagon to a binge later if you actually cut all 'syn' stype food out...I don't do slimming world and have never tried it, but I have one 'cheat' day a week, Sunday....I eat what I want (normal portion sizes though, not an excuse to binge or pig out)...it keeps me from wanting to binge or eat silly things in the week...