In an ideal world, you'd buy the things you need once and then keep it for life. Then life happens. You need to move, stuff gets old or you need to upgrade. Before buying something, consider how much it would cost to get rid of it if you had to.
Some things are harder to get rid of than others. Your old smartphone has a lot of uses, but getting rid of a couch probably means finding (or being) someone with a truck. The cost of getting rid of items can start to climb, if not in money then at least in time. If you're trying to determine whether a particular purchase is worth it, ask yourself how much it would cost to get rid of it later. And, perhaps more importantly, how soon you'll need to do so. As personal finance blog Under the Money Tree explains:
The thing that stuck me most was how much effort it was to get rid of all of this stuff. Time spent listing things on eBay, time spent in the post office, time spent rummaging around the house… The effort to get rid of all of this stuff was so much more than it took to acquire/collect it all.
Some things will be worth the cost. If you bought a lightly used couch, owned it for 10 or 20 years, and only had to move it when it was finally time to get a new one, the rare occasion you need to get rid of it is a negligible expense. However, if you paid $100 for a used couch that already has holes in it, you'll probably waste more than you paid for it just getting it out of your home in a year's time when you get sick of sitting on the flattened cushions.