The role of canon

Canon provides a common framework of reference in any context. A complex fiction universe, such as the Star Trek one, benefits greatly from having a canon and adhering to it. On the one hand, a carefully created, complex word creates the basis for unlimited stories told within its framework. Even if it is just a short or loosely linked story, fans can understand it having the common background of the canon. On the other hand, it makes the life of creators of new series, spin-offs, authors of books taking place in the universe much easier. They only have to focus on their story, the universe, the common framework of reference has been created for them. As we use reality as a common reference framework, a fictious canon can have the same role. Given such a complex framework, it is not difficult to imagine detective stories or even chick lit set in this universe. Why not?

At the same time, fiction writers have experimented with bending the boundaries of the real world, too. Similarly, in order to not have your imagination be bound by the Star Trek universe, you can also create stories that do not adhere to the canon, thus enriching it by introducing the 'what if' into the discussion. We all know that Star Trek is fiction, but as it is taking place in the future, it may even prove to be partly correct. What if mankind will have taken a different route in a few hundered years? Actually, Discovery has already started experimenting with this when creating a fully paralel universe.

Most canons are also formed according to the wishes of the masses. It has happened to Christian biblical canon, but also happens in fiction. Charles Dickens was famous for continuing the story of his serialised novels according to reader feedback. I guess it has happened in the Star Trek universe, too. Probably the most famous such deviation from story line has been the death and non-death of Spock. 

In my opinion, Star Trek is adhering to the canon better than other series, probably as a result of a very complex preliminary world buliding by Gene Roddenberry. Having much fewer discussions on coherence than for example the Star Trek universe, it is far easier to broaden the franchise, and to build a steady fandom.