The reason it’s this way is because if, for example, you get paid £1500, but then £750 goes out immediately on rent, the dial would show that you’ve already spent half of your money for the entire month.
On the flipside, if your rent didn’t go out for another three weeks, for most of the month the dial would show that you have £750 more than you actually have to spend. By excluding any standing orders, you have a more accurate figure of how much spending money you have.
You can also manually flag transactions that you don’t want the dial to take into account.