For some reason, a fellow-consultant dropped in to visit me; we sat in the living-room and chatted.
During the conversation he told me that he did not leave his office without charging someone.
The gist was that he would discuss matters on the phone, sitting in his office, for free (presumably with some sort of time-limit), but that any thing that required his physical presence in another place, expressly, that required that his brain, eyes, hands and mouth were present, was important enough to warrant a fee.
I am considering implementing such a philosophy here, albeit twenty two years later.
If you are a consultant, then satisfying people with your physical presence suggests that your physical presence provides something that cannot be otherwise obtained.
And that suggests that you have something of real dollar value in you when you visit a client.