There is one central, screamingly obvious factor that impacts programmer productivity. It is unknown, ignored and/or undiscussed. But it matters more than most other factors. It's the ABP factor, "Anything But Programming." When a programmer isn't programming, that programmer isn't, well, writing code. I don't care what that programmer is doing! If it's ABP, that person is not -- repeat not -- writing code!
The ABP Factor
If your job is reading, any time you don't spending reading is time you're not doing your job. Call it anything you like: getting ready, preparing, taking a break, recovering, digesting, blah, blah, blah. Whatever you call it, if you're not reading, you're ... (get ready now) ... not reading! You're doing something else.
If your job is cleaning the house, any time you spend not cleaning the house is time you're spending not doing your job.
I hope you get the idea by now.
Understanding the Status of ABP
Non-technical people, people who don't program, people who used to program but don't any more and people who still think they're programmers but have regressed to a lower form of life (like managers) often value what they can do (which is clearly ABP) highly. Makes sense. If you do it, it must be a good thing. If you can't, don't or won't do it, it must not be the kind of thing really valuable people like you do. This applies to programming in spades. ABP is highly valued. Programmers quickly get the idea that the way to increase your status is to spend increasing amounts of your time indulging in that valuable thing, ABP.
Is ABP Worth Something?
Putting my cynicism aside for the moment, the answer is a clear, resounding yes. A certain amount of planning, coordination and other stuff is necessary. Not doing it well leads to really bad things. It's even OK for some people to spend most of their time in such non-programming activities!
But let's make it even clearer. Think about manufacturing or customer service. Either you're directly contributing to the production of goods or services, or you're not. If you are, we can start talking about how effective and efficient you are. If you're not ... either your personal productivity is lower than it could be or, much worse, you're overhead!!
Are you writing code? Good. Then we can have a grounded discussion about your productivity -- at least you're trying; at least your shoulder is at the wheel and you're pushing. Are you doing ABP? You're probably self-important overhead; stop wasting my time and yours.
Maybe you really are doing something that makes productivity better in some mysterious way. I'm open to the possibility! But the burden is on you to prove it.
Personal note: I spent most of every day writing code for a couple decades. I know all about programming overhead. I was acutely conscious of my personal overhead, and contributing to other peoples'. Now I don't write code. I feel guilty wasting the time of programmers. The only way I can justify it is if, as a result of our interaction, their productivity goes up, so that the time spent not programming ended up being a net productivity increase. I always think: minimize the time, maximize the value.