Hair clippers vs. beard trimmers
Depending on the type of beard, trimmers are used to maintain the beard, trim the edges of the beard, or trim body hair. They are designed with great precision and often don't have the energy needed to cut thick hair or long beards. That's why you'll notice a big difference in the size and shape of many parts between pruners and scissors.
If you try to cut a lot of hair with a small trimmer, it can get stuck, pull your hair, or overheat. It's like clearing a jungle path with a kitchen knife.
Good hairpins, on the other hand, cut the thickest hair seamlessly and evenly. You can then use a smaller trimmer to shape the edges, or as an intermediate step before using a razor or electric razor.