I have the following circuit

It's a basic traffic light circuit using a 555 timer and decade counter. All works fine but what is the purpose of the 0.1 microfarad capacitor on the left of the diagram? As far as I can see it's doing nothing. If I remove the capacitor or replace it with a 10 microfarad or 100 microfarad nothing changes.

This diagram has been provided to me so guessing that it does serve a purpose but what is it?

Thanks