The purpose of wax is primarily to protect your finish and secondarily to enhance your car's shine. If your car's finish is in good shape, some people argue that wax can't make it any shinier because it just adds a layer on top of the perfectly shiny finish. Other people say that true wax (as opposed to synthetic products) has enough dimensionality that the wax can fill hairline scratches and create a smoother surface which is therefore shinier.
There is also such a blurry line between "wax," "polish," "sealant," "glaze" and other kinds of products that it becomes hard to say whether a car that has a polished finish has any "wax" on it!
Before we go any further, let's define our terms.
Wax. "Wax" refers generically to any substance you put on your car's finish to protect it from the elements. When the term is used specifically and literally, "wax" refers to products containing carnauba wax, which comes from a palm tree. Carnauba is universally the wax of choice because it's the hardest naturally occurring wax, and it has a high melting point (for a wax). In its natural state, carnauba is hard as a brick, and you can shave flakes off as shown on the left. Because it's so hard, carnauba must always be mixed with other substances to make it usable. The highest concentration of carnauba a car wax can contain is about 30%. That means that putting solvents, oils, cleaners, polishes, etc. in the "wax" is inevitable because the manufacturers have to mix something in with the carnauba or it will be unusable.
Polish. This is used carefully to mean two different things and sloppily to mean anything in the general vicinity of a car care product. The first careful meaning is an abrasive compound that can be used to smooth out a car's surface. The second careful meaning is a synthetic, non-wax product that serves the same purpose that a wax traditionally serves, i.e., protecting the car's finish. The word "sealant" is more commonly used for this meaning.
Sealant. Sealant normally refers to a synthetic wax-like product that doesn't contain wax.
Glaze. Same as sealant, as far as I can tell. Sometimes seems to imply that it's a sealant that contains some polish (i.e., abrasives).
The Wax vs. Synthetics Debate
There are big debates among detailing nuts about whether waxes are better or synthetics are better. This debate is muddied by the fact that many products contain both natural carnauba and synthetic ingredients.
The general feeling seems to be that waxes are harder to apply, harder to remove, and don't last as long, but they can produce a rich, warm deep glow that synthetic products can't match. In contrast, most synthetics are easy to put on and take off, and some of them last a long time. They have a much higher melting point than wax, which is helpful on a car's surface which can get pretty hot. They can produce a near-perfect, highly reflective surface, but some feel that the shine lacks depth and is ultimately without "soul." (Some people really take this stuff seriously!) I personally am not convinced. I have gotten a "nice warm glow" from both wax and synthetic products. I think the glow has as much to do with the surface preparation as with the wax.
Some real detailing fanatics apply a bottom synthetic coat for long-lasting protection and then apply a wax top coat for that deep, warm glow. AutoGeeks has a good summary of the debate.
