Waist shorts are a great choice for shorter rides under two hours, indoor training sessions, or hot-weather riding when you want maximum ventilation and easy on/off convenience. They're also ideal if you simply find bib straps uncomfortable or dislike the feeling of suspenders on your shoulders.
The main trade-off is that the elastic waistband can roll or create pressure points during longer rides, and the chamois pad may shift slightly when you're riding aggressively out of the saddle. For rides over a couple of hours, most cyclists find bib shorts more comfortable since the straps keep everything locked in place without any waist restriction.
That said, waist shorts shine for their simplicity—quick bathroom breaks, easy to throw on for a spin class or commute, and no need to remove your jersey to take them off. If most of your riding is under two hours or you prioritize convenience, waist shorts are a solid pick.