Once the ritual is complete the Powers are thanked and dismissed. This begins the withdrawal of consciousness back to its pre-ritual state. The final steps are closing the Gates (thus sealing off the altered state of consciousness) and closing the Circle (thus returning to the everyday world). The Circle should not be closed if there is any suspicion that the withdrawal from the altered state has not been completed fully.
It is sensible to undertake a 'sanity check' between closing the Gates and closing the Circle.
It sometimes happens that although the magician goes through the steps of closing down, the attention is not engaged, and the magician remains in the altered state. This is not a good idea. The energy of that state will continue to manifest in every intention in everyday life, and all sorts of unplanned things will start to happen. A related problem is that every magician will find sooner or later an altered state which compensates for some of their perceived inadequacies (in the way that many people like to get drunk at parties), and they will not want to let go of it because it makes them feel good, so they come out of the ritual in an altered state without realising they have failed to close down correctly. This is called obsession, and it is one of the interesting difficulties of magical work.
Closing down correctly is important if you don't want to end up like a badly cracked pot. If you don't feel happy that the Powers have been completely dismissed and the Gates closed correctly, go back and repeat the steps again.