The reason that carnauba is used is for its highly reflective qualities and durable finish.
To quote Anne Marie Helmenstine, Ph.D. from About.com:
Carnauba wax has a very high melting point of 82-86 °C (180-187 °F). It is harder than concrete and nearly insoluble in water and ethanol. It is non-toxic and hypoallergenic.
You would be surprised, carnauba is used in many food and other items you use every day. Carnauba wax leaves a better finish than most paint sealants. Wax lasts anywhere from 6 to 12 weeks depending on factors such whether or not the car is garaged, how it is washed and the soap used (by hand or run through a wash), and the weather conditions.
Different waxes have different properties in terms of finish and the ease of application. Many companies put their own marketing "spin" on to naming variations of waxes in order to sell more products. This is one reason for the confusion when it comes time to pick a product to use. When it comes right down to it, consider how easy it is to use, the resulting finish and how durable it is - which ever factors are important to you.
GlazeThink of glaze as a product that hides defects such as fine scratches in a car's finish by filling in and leveling the surface. Glaze has virtually no protective qualities. The longevity of a glaze is very short only a week or two at best and is easily washed away. Body shops will use a glaze as a final step prior to delivering a vehicle. It is very popular to use a glaze as a final step prior to using a wax.
Think of a paint sealant just as the name implies. A paint sealant lasts about twice as long as a wax, but most of them lack the deep, rich brilliant shine that a carnauba wax provides. Paint sealants bond to the surface with polymers for a protective coating.
In some cases, paint sealants can make the defects in the paint stand out. There are many differences of opinion on paint sealants as there is on about any other topic in car care. Too many to be covered here in this post!
Polishes do not have any protective qualities like a wax or a paint sealant. Polish is used to correct minor defects in a finish as a final step.
Think of a compound as a polish on steroids. A compound does much of what a polish does but is more aggressive and abrasive.
Compounds are for removing heavy deep scratches, sanding marks, layers of oxidized paint, and other heavily embedded contaminants in the finish. Because they are more aggressive than a polish, compounds level out a finish much quicker. Depending on how aggressive the compound is, a polish usually is used afterwards as a final step in buffing.
Hopefully this helps clear up some of the confusion out of what are wax, glaze, paint sealant, polish and compound. There are also some products that are "hybrids" that designed to perform multiple tasks in one step to save time. As we say "Keep It Simple" - don't let the terminology and marketing spin confuse you.