[OJFord]

I like to distinguish complexity from complication: the former requires cleverness to understand more of; the latter time and effort.

In the simple case of a solo project, as much complexity as you understand is fine; in a team you obviously need some idea of a threshold, not that you could quantitatively define it. Complexity isn't necessary, though isn't a problem - complication on the other hand is always bad, it's just making things hard to reason about, but may be necessary if the only alternative is adding unacceptable complexity.

The problem with discussing 'simplicity' is that it's an antonym for both complexity and complicatedness.