If you believe that code will help someone with understanding (yourself included) then it is necessary. It is needed to help with clarity. It may not be strictly required for the correctness of your program, but your goal should not be to express the correct solution as succinctly as possible. That approach leads to many other problems.
Occasionally I include solutions for problems which have not yet been uncovered. Those methods may not be called (dead code) and any kind of static analysis would report them as "unnecessary." If I make the decision that such code will help me, or help someone else, later then I believe it is totally necessary, and good to include. Worse-case is that it will be a good starting point for someone later, and they will throw it away and replace it with something better.
Never include unnecessary code. If there are incorrect implementations that you are replacing, remove the incorrect ones! Don't leave traps lying around for people to get caught in. Unexecuted code, or not succinct code, is not unnecessary. I constantly include semicolons, and brackets around one-line conditionals - those are defensive practices which are designed to prevent future problems, and aid in clarity.
This is why people are hiring you - to apply human intelligence and judgement to a problem. There are situations where doing not strictly necessary things is appropriate, and situations when doing not strictly necessary things is a waste of time. It's up to you to decide. Different actions are necessary for different metrics. One thing may be necessary for a correct solution, and another thing may be necessary to help someone else understand your correct solution. Everything should be useful (necessary?) under some kind of metric.