A guide to saving: Frivolous versus Serious?

During a conversation with a friend the other day, she mentioned that she has two types of money: frivolity fund and serious savings. The excess money she earns every month is her frivolity fund, to be spent on things that she likes the look of, once the important things like her mortgage and food shopping have been paid. The cash in her savings though, is serious savings; it’s there for a purpose and it can’t be spent on expensive frivolities, no matter how badly she wants them. Her main problem is that she doesn’t really know what her serious savings are for.