I wish it didn't. Life would be much simpler. But it really does.
Wearing different clothes, driving a different car (or not driving a car, riding a bike) has an enormous impact on the impression that you leave on people.
It's not necessarily 'spend more win more'. A fancy car might not ingratiate you with the locals.
Beyond that - I think you have to unpick what is meant by "don't need". If I were restricted to buying things I need, I'd be donating something like 80% of my income to charity.
There are interesting cases - like why someone who really can't afford a particular thing buys it anyway - but usually that sort of thing, in my experience, comes down to a type of stress that has them making suboptimal decisions all over (e.g. if you're poor, everything is harder, because everything is stressful, and...)