There are good and bad parts of booking back to back. We did a 3+4 last year and have a 3+7 later this year. To us, the cruise felt a bit more like a repeat. Same shows, same dinner menus, same trivia, etc. BUT you can certainly take a more relaxed pace.
When you do a back to back (port canaveral) you only pay for parking for your first cruise, so you get free parking for the second one. If you leave the terminal building for any reason after the first cruise, they will not let you back in until it officially opens. So you can't take advantage of early check in and boarding if you go to your car for any reason. You can basically get whatever dining preferences you want for the second cruise. The head server will come and confirm your second sailing. You can change servers, rotation, and dining time with no issue. We will be in the same room this time, where we were not last time. There was no problem transferring our luggage and our room was ready as soon as we got back on board the ship, as we had already met our new stateroom host. Many of the cruise staff will remember you so that is useful as well.