What is the "categorical coefficient" and what can I use it for?
The categorical coefficient is only applicable for non-scaled multi-state characters, i.e. characters that can present more than two possible states. For example, color is multi-state. The color of a specimen could be red, green, or blue. You can categorize these color states by 1, 2, and 3, respectively. Any coefficient other than the categorical would consider 2 closer to 3 than 1 is to 3. The categorical coefficient considers any different state as no match, while any same state is a full match.
An example is the existence of different serotypes. Each serotype can be assigned a number, which does not imply any relationship between the serotypes. Multi-locus enzyme electrophoresis (MLEE) or multi-locus sequence typing (MLST) are other examples.
It makes no sense, and is even incorrect, to use the categorical coefficient for any other data type than multi-state characters as described above.