When you call for a free estimate whether it be for a repair, whole roof, roof cleaning, etc. I personally come to your home, evaluate your needs and measure your home with a tape measure not with satellite images like a lot of the other guys.
I believe it is important to personally visit the property. That way I can see every aspect of the home and its surroundings. How many layers of shingles are on the roof, do you have a satellite dish on the roof, do you have a chimney, how many pipes are on the roof, do you have any brick flashing, does the brick flashing need to be replaced with the roof, what does the ground look like (trees, shrubs, a/c units, pools, etc.), and everything else I need to about. All this is why I like to do an onsite estimate.