When we think of oxidization (milky haze on dark colored vehicles), snow brush marks and spider webbing (fine scratches) these are vehicle paint characteristics that require paint correction.
In order to restore the vehicle paint to as near original condition, the use of a buffer is required. A buffer enables the buffing pad and compound (lubricant) to cut-into the clear coat at a fast revolution speed to heat-up the paint surface and correction the paint blemish.
Polishing is typically the final stage in the high-speed process and is applied by buffer at lower speed (not enough to cut-into the clear coat). The idea is to remove any residual trailings created during the high-speed portion of the buffing process. This can also double as an "express buff" to correct minor blemishes such as snow brush markings.
The analogy of applying sunscreen to your skin in order to reduce the effects of a sunburn can be applied in similar context to paint protection for your vehicle.
Applying either wax or paint sealant to your vehicle paint adds a barrier between the paint surface and the natural elements. This barrier helps protect the paint from oxidizing and degrading (which can occur over successive winters with no paint protection).
Wax is typically comprised of carnauba (organic based) extracts, which pull the shine out of the vehicle paint.
Paint sealant is a synthetic blend, intended more for longevity over shine.