Optimization has a price, no matter what the results are. When a piece of code works, it might be better (sometimes) to leave it alone than to try making it faster at all costs. There are a few rules to keep in mind when doing any kind of optimization:
Make it work first
Work from the user's point of view
Keep the code readable
A very common mistake is to try to optimize the code while you are writing it. This is mostly pointless because the real bottlenecks are often located where you would have never thought they would be.
An application is usually composed of very complex interactions, and it is impossible to get a full picture of what is going on before it is really used.
Of course, this is not a reason to write a function or a method without trying to make it as fast as possible. You should be careful to lower its complexity as much as possible and avoid useless repetition. But the first goal is to make it work. This goal should not be hindered...