In triathlons, anything that helps quicken transitions and maintain your energy levels benefits your overall race. The more competitive you become, the more likely you are to forgo putting on number-tagged tops in favor of trisuits. You won't want to pin a number on a trisuit—and pins can be annoying enough to deal with on their own. Racing belts alleviate this issue by easily clipping around your waist and securing your number with toggles or clasps.
Some racing belts even come with pockets for fuel storage. Longer tris will demand more gels and liquids to keep you going—and aid stations won't be at every corner you need them. A racing belt that comes equipped with fuel pockets can be a great investment for longer distance triathletes. You not only shorten transition times with a quick-fastening belt, but can stow more fuel as you race.