I don't think everybody _needs_ one but they're extremely handy to have, especially when you want something very particular, like a missing part of a cheap tool, a new handle for a particular broom, a doorstop that works with your weird door, plastic feet that fit your specific furniture or a desk organizer that's the specific size needed for your desk.

And even if mass a produced version of these things would be cheaper/better, often you just won't be able to find it.