The issue with the method of "just show up" is if you are visiting a dropzone on a trip there might not be many people there, or many people in your experience range on that given day, so being able to reach out beforehand could make for a much more enjoyable visit being that time is limited. Not to mention, even if it is your local dz, you might never meet certain compatible people that jump different days than you, but if you could connect online you might adjust your jump days to meet up with new people.