What is the difference between "with overflow" and "without overflow" drains?

WHAT IS A DIFFERENCE BETWEEN "WITH OVERFLOW" AND "WITHOUT OVERFLOW" DRAINS?

An overflow opening is a small hole drilled in the top of the threaded portion of the drain that allows overflow water from the sink to enter the drain pipe. If your sink features an overflow, it is very important to purchase a drain with an overflow opening so that your sink and drain function properly. If your sink does not feature an overflow hole it needs to be paired with a a drain without overflow.