Why uncap frames
In days of olde, honey comb was simply crushed to extract the liquid honey.
It takes bees a large effort to build the wax comb, and they consume considerable honey to create the wax. Once built, they can fill it with honey in a very short time, and it can be re-used for many years. For this reason, your comb is one of your most valuable resources.
The most efficient method to extract the honey, is to spin it out using centrifical force (see extractors). Each cell is sealed with a wax capping which must be removed before the honey can be extracted, hence the term - uncapping.