There has been some debate in recent times regarding the importance of the License to Depart, and, if, indeed, it is needed at all. While some make arguments for the latter I personally believe the License to Depart is necessary for good practice of ceremonial magic. Yes, ceremonies can still work without it, but I think they work better with it, and it's included in most grimoires and traditions for a very good reason.
Sometimes it is not employed due to pure laziness, while other times it is not employed because the magician in question believes it negates the effects of the previous invocation. Others dislike the idea of telling spirits to "get the hell out", but really I believe this shows a lack of understanding of what the License to Depart actually is. A License to Depart is the giving of permisison to leave (i.e. they are required to stay the length of your working for whatever your need is), not a command to leave. If they fail to leave (most genuine entities will not), then follows the banishing to remove them and anything else. Thus a banishing can still be quite essential even after a License to Depart is employed. Usually when a Divine Name ruling the spirit in question is employed in the License to Depart (for example: "depart in peace in the name of [Divine Name]") there should be no issue with the spirit leaving. A general banishing may be appropriate for other stray energy or elementals attracted by the ritual.
Some form of "closing" is essential for the sanity of the magician. To not close (in whatever fashion) means that the mental state and magical energy raised are being brought into one's everyday life. If a magician opens, then they should close. It would be like not removing one's robe after a working. The initiation ceremonies of the Golden Dawn employ an Opening and Closing for a very good reason, and just as we employ the structure of these rituals (particularly that of the 0=0 in the Z-2 formula) for our ceremonial work, so too should we employ a suitable Opening and Closing (points E and X of the Z-2 formula).
A general formula for writing a License to Depart is as follows:
- Thank the entity for showing up, particularly in the case of Angels, etc.
- Ask the entity to depart in the name of a higher power (in much the same way you would have asked them to appear by such a name).
- Add a clause for peace between the entity and you ("May there be peace between us").
- Add a blessing to the spirit if suitable, particularly depending on one's religious affiliations ("The blessings of God/Yeheshuah/the God and Goddess be upon you").
- Close with a suitable phrase or word ("In the name of... Amen").