Purely from a sovereignty points of view, it makes a lot of sense if you think your country being independent is important.

From an economic point of view, it will probably never make sense because the UK was shielded from most of the EU most stupid decisions through carve out. They were out the disastrous currency union. They were not fully in Schengen. They had a lot of leeway with regulations.

Coming back would probably be a mistake however. They would most likely be forced to join the eurozone.