The method and neatness of the closing of the cell, when it is full of ripe honey, varies considerably from colony to colony and race to race.
We beekeepers set great store by the quality and appearance of the wax cappings. This is also reflected in the price that customers are prepared to pay.
There are racial differences in the regularity of capping and the appearance of the resulting honeycomb. So it is a valid criteria for assessment when trying to decide on selection for breeding of one colony against another.
White cappings are generally the most highly prized, and those that have a small airspace and slight doming are the highest prized of all.
Greasy cappings are not actually slippery, they just have a greasy appearance. There are no airspaces and the wax is often a yellow colour. Comb of this type can be used to form chunks for inclusion in "Chunk honey" as it is less likely to retain air bubbles on its surface as can happen if domed white honeycomb cappings are used.
Cappings quality, is very subjective in assessment... I know that my opinion of what looks best does not line up with some honey judge's opinions, but I may be biased in favour of my own produce.
Regular cappings, under show rules, are those that are all of exactly the same size. There are some judges that prefer worker sized cells, but providing that all cells are the same size (100% drone or 100% worker) then the entry should not be discriminated against. The cells for show purposes should be in exact horizontal alignment.