The question of whether encryption is appropriate for a given project is a tricky one.
On the one hand, if you distribute an unencrypted DCP it is easy for anybody to take it and do whatever they want with its contents. They could use DCP-o-matic to convert it to a MP4, show it in their cinema, or even edit and redistribute it in ways that you do not like.
Encryption prevents this, but brings its own problems. It will be impossible for a cinema to screen your DCP unless they have the correct KDM. This is easy enough if things work as they should, but problems can occur. For example, cinemas may substitute broken playout servers with new ones without telling you: then the KDM that you sent them will be invalid, and a new one required. If the cinema can't get in touch with you, or somebody else who can create a new KDM, they can't screen your DCP. Often these problems are only discovered very close to showtime, with little time for fixes.
If you are distributing encrypted DCPs widely it is worth thinking about who will make the KDMs, and who will provide quick-response technical support. It may be a good idea to engage a company who can provide such services.