I am a corporate chaplain. I have a home office from which I answer emails, make calls, file reports, study,and have couples in for premarital counseling. I also store materials that I pass out and have a library that I make available to employees I serve. 
I work for a company and am contacted out to serve several companies. My company's main office is in another state and I do not have office space there. I do not have, nor am I offered, office space at any of the companies I serve. I make regular, weekly and bi-weekly rounds at the companies I serve, attend and preform weddings and funerals. 
There is discussion as to when mileage should start. Some are saying mileage starts at the first location; others say it starts from the home office. Which is it? This is important because some locations are 35 miles away.