So I get this idea is coming from the perspective of controlling your finances.
I immediately think about situations where this would unintentionally backfire. Travelling late at night, need food and sustenance, only option is Pret… travelling early in the morning, only option is Pret… colleague decides to have a meeting in Pret … etc etc. There’s just too many situations where this type of function would be more trouble than it’s worth. Cue messages to CS from people saying: hey I blocked Tesco/Pret/McDonalds but I now need to make a purchase in the next 30 seconds as it’s the only option available to me.