Sometimes there’s no substitute for hand sanding. When you need to sand spindles, complex shapes, and tight corners you sand by hand.
Hand sanding allows you to closely follow the intricated shapes of your workpiece, adapt the pressure, avoid over-sanding, and give your workpiece that perfect final touch. Where precision and even pressure are required hand sanding is still the best option.
But hand sanding takes time and can get quite strenuous. Standard sanding sheets clog and wear out fast. They tear, break, and lose their grit when you fold them to reach corners and sand edges. They can rarely cope equally well with different materials: metal, hardwood, epoxy, or plastic.
When you sand complex shapes and more than one material, a single sanding sheet is rarely enough.