Why are simplex channels designated in the VHF/UHF band plans?

Simplex communication involves transmitting and receiving on the exact same frequency, bypassing a repeater. Band plans designate specific simplex channels so that stations in close physical proximity can communicate directly without unnecessarily tying up a repeater system. Repeaters are designed to extend range for operators who cannot hear each other directly. If two stations are close enough to converse on simplex, they should use a simplex channel to leave the repeater open for long-distance, mobile, or emergency traffic. Simplex channels are entirely separate from repeater inputs and are not restricted to just contesting or DX work.