I don't have any specific use case for making the statement cache optional. I expected that by changing the cache size to 0 there will be no statement cache. I think that this is a common assumption as can be seen in https://github.com/ghaering/pysqlite/issues/126#issue-346189937.

rogerbinns did give a use case where we would like to disable the statement cache in https://github.com/ghaering/pysqlite/issues/126#issuecomment-410030910. I think that statement cache should be disable implicitly in that case as you suggest. The code change will be very similar and I do believe we should allow the user to disable the cache. I will be happy to open a new PR once this is merged that will disable the statement cache implicitly when calling `set_authorizer()`