There is no justification except fear of not having enough money. The issue is whether you can meet your peak budget. If you can get by with $x * 0.80 most of the time, but every once in a while you really, really need the full $x then you spend $x/year. Because, if you don't, that extra $x * 0.20 will be cut (possibly even more). This leads to an increasingly tight budget (or it's feared at least) so it's "better" to be wasteful.