Most people who work out in a public gym will agree to a fact that finding a weight or a dumbbell of a particular weight takes up a lot of time. One of the major reasons for that happening is the weights not being racked properly. Leaving weights everywhere around in the gym makes it a hassle for everyone and is one of the worst things to do in the gym. Every place has a etiquette and a gym is no different.
Typically every gym arranges the weights either by naming their dumbbells and racking system or by arranging them from lowest to highest in accordance with their weight. It becomes easier than to trace the dumbbells and use it while working out. Certain gyms also have a rule book that specifically mentions this as a rule.