The point of developing a trait or any skill is to become more proficient at it such that you can apply it when you need it. It is like learning different languages. Your mother tongue might be English, but it doesn't mean you cannot learn fluent Spanish or French. You might not naturally use the two, but when you need to you can. More tools in your belt really.
I've actually actively try to develop my weaker functions... Mostly Ti, Fi, Se.
In response to Night and dissonance, a tool is a tool as long as it works. It makes little difference whether you call it Fe or Fi. As long as it gets the job done. Does the distinction between Fe vs Fi matter?