How do you feel about being late? Are you a timely and prompt person? Early, even?
Do you push things until the last minute or do you leave yourself a little margin for traffic, parking, getting lost, etc.?
How do you feel when you have an appointment and the other party is late? Are you understanding or annoyed?
Of course, emergencies and unforeseen problems come up all the time, and for the most part, people are sympathetic and accommodating. But you should not rely on that being the case.
Being on time for an appointment is a sign of respect for the other party. Making someone wait is rude and implies that your time is more valuable than theirs.
There are so many other variables that can make someone like you or want to do business with you (your presentation, your demeanor, your dress, your communication skills, your products and services mix, your prices), that you shouldn’t negatively affect their impression of you by doing something as silly as being late.
If you must be late, by all means call and give the other person the chance to reschedule if necessary. Again, it is simply a matter of respect.
Until we win the lottery or become independently wealthy and can afford to “Waste Time” we should continue to be prompt appointment-makers.