When I was a small child, my grandfather would tell us (upon one of our lengthy summer visits), "It's nice to see you come and it's nice to see you go."
When I was that age, I thought that was the meanest thing anyone could say until...
I had grandchildren and realized how fun (and taxing) a visit from a herd of grandchildren could be. Now I understand the wisdom in those words.
Then, of course, there are the wise words of Ben Franklin/Poor Richard, "Fish and visitors smell in three days."
Yep, don't overstay your welcome.