yes, it is, Visitor, thanks for asking.
it is necessary, you see, for practical purposes.
those Categories are based on communication practices and are as follows:

A (Addicts) - people who feel compelled to communicate ceaselessly, via "social" media, phone etc

B (Business) - normal business practice is to respond to communications (like email) within 24-48 hours

C (Casual) - not reliable, but will generally get a response or some kind in a week or two, maybe three

D (Disfunctional) - you never know when you hear back from those people (if ever)

i place myself in the B Category and make a deliberate effort to avoid people in the D Category, those people can be a cause of very significant time loss, plus, generally, they will get themselves and those around them into trouble, sooner or later. alternatively, they will spend their life living under a stone - i accept that as their personal choice.