When I built my boat dock I made sure to make it tall enough that I could leave my tower up. The problem that I discovered by doing so it doesn't provide a lot of protection from the rain and sun. Anything but a straight up/down rain or a noonday sun still exposes the boat to the elements.
I have found that if I fold the tower down and crank the lift up higher it does provide better protection. However, I like to get in the boat, crank down the lift and be on the water in 2 minutes or less, so I am trying to find a boat cover to provide a little more protection.
The covered boat dock does keep the birds and bird poop off the boat and it does protect it more than being uncovered, so overall, I think it was a good investment.