Money saved by one person may be time spent by another.

Savings often move rather than disappear. The cheaper option gets cheaper because somebody assembles it, queues for it, drives further for it, or waits in an afternoon that was not counted anywhere. Within a household this is common and rarely discussed: one person economises and another person absorbs the hours, and the budget records only the first half.

Ask whose time is funding the saving before deciding it was a good one. Sometimes it clearly is, and sometimes forty pounds is being paid for with a Saturday. If the time is somebody else’s, they should be part of the decision.