The best way to answer this question is to understand what you are trying to accomplish, on what color and type of vehicle.You will find a great variety of answers depending if you are dealing with a show car or a daily driver, a white vehicle as opposed to a dark one.
A wax is normally defined as a natural base product (carnauba wax, bee's wax etc..) in combination with natural solvents and polymers (100% natural wax), or in combination with synthetic or petroleum based solvents or polymers (or chargers), which is referred to as a hybrid wax. To the trained eye, these products will provide more depth, warmth, a richer glow when applied. The drawback is that it does not last but 1-3 months (depending on exposure, heat, humidity and detailing regimentation)
A paint sealant is referring to as a fully synthetic product which thrives in technological advancement. Although it does boast longer protection (6-12 months) and more chemical resiliency it does have the drawback of looking "flat" and uni-dimensional
The purpose of wax over sealant or wax over coating is to have "the best of both world" (ie. the superior protection on the bottom and the superior optical qualities on top). Your game plan will have to be tailored to the vehicle you are working on. If you are dealing with a single stage white daily driver, a wax over sealant will be an overkill and will not give the WOW factor to your client. You may be able to discern the subtleties but they won't find much comfort in the upsell. On the other hand, if you are dealing with a "Saturday" car (ie. a garage queen, weekend driver, local show car), then you will definitely have a leg to stand on with your wax over sealant game plan. Now if it is your personal vehicle, then do what you see pleases your eye best regardless if is a SS white daily driver (since detailing at that point is to cosmetically enhance to your eye's delight). A little experimentation will go a long way