Unretirement is certainly a major step. Your booze is gone. Your cabinets and chests are un-built. Your stockpiles are messed up. Room designations have to be re-done. Animals are scattered. It's quite a bit of work with a mature fort, though not a big deal with a new fort.
Now consider the upside to retirement. Suppose that you have an excellent fortress with legendary craftsmen, battle-hardened soldiers, and fabulous wealth. And your fortress is dying from low FPS and data corruption causing CTDs. You want a fresh FPS without starting from scratch.
So start a new fort close to the old fort. Dig a few rooms. Build a few pedestals. Retire the new fort. Start an adventurer with a pack animal. Haul your high-value items from the old fort to the new fort. You can haul as many as you want, though not more than about 500 at a time.
Now unretire your new fort. Cleanup is minimal, because the fort is so young. You have a fresh FPS. You have piles and piles of useful items that you've brought over. And most of your migrants will be high-skill dwarves from your old fort. Your new fort will develop much faster than if you had started from scratch.
Maybe this approach lacks the usual drama and desperation of seven inexperienced dwarves striking the earth. But it also enables much grander projects than are possible in a single fort, such as taking over the world.
Here's my checklist for retiring a fort.
Edit: Fixed link.