Naive implementation and user-friendly implementation

While reading codes of NZMATH, I've noticed there are many cluttering type checks and such for user-frienliness. For speed up in the future, they seem to be going to become an obstacles; it is better to asuume the validity of inputs. In other words, 'implement naively.' On the other hand, the user-frienliness was introduced for users' (or developers' as well) convinience, and it is not negligible factor.