SW seem to have changed their stance on this. The old website used to say it was okay to use syns weekly, now they advise to use them daily and don't save them up
At Slimming World we don't recommend that you save all your Syns up for the week, just so you can have a few drinks on a Saturday night. Depriving yourself throughout that week is like putting yourself in a tight corset. Before Saturday night arrives, that corset could well have been flung off, and your eating plan been pushed aside for the week…then the month… then the year.
Food Optimising means that you can allow yourself a flexible Syn day once in a while, and not have to save up Syns beforehand, or deprive yourself afterwards.
I don't save up, never have but the advice from SW is above.