You should favor readability
Among the books I am currently making my way through is "Exploring Computer Science with Scheme" by Oliver Grillmeyer. The publish date on this particular book is 1998. No matter how often it happens, I feel a twinge of despair for our profession when I read sound advice from a decade or more ago that has yet to be widely adopted; or worse is still hotly contested.
Grillmeyer contrasts a couple different functions that accomplish the same end. One terse, but obfuscated; One verbose, but transparent. In conclusion, Grillmeyer states, "In a tradeoff between readability and length of code, you should favor readability."
Sure, you can use some Ruby-fu and get those four lines in the controller down to one. Yes, you can in-line the whole damn method call. But to what end? For what purpose? Why are you reducing the lines of code? What is your objective?
Favoring line count
I once completed the Bowling Kata in Ruby. It was approximately twenty five lines of code. It was readable. Each method had a clear and singular intent. I asked a non-developer friend to look at it and tell me what it did. It took him no more than 60 seconds to figure it out. I then told a Ruby developer about the Kata and without even looking at the code he said, "You should be able to do that in seven lines of Ruby."
So I set out to refactor the code down to seven lines. And it was an interesting exercise. I managed to get the code down to about twelve lines; I had cut the code in half. But then I stopped. The intent was no longer clear. One had to interpret the code in order to discern what was happening. My tests were a mess; I could not test behaviors in isolation.
I had sacrificed clarity at the altar of line count. And I was ashamed.
A (very brief) twitter discussion
What if no one reads it?
So you're working on a pet project; something that only you will ever work on. No other developer will ever see this code. And you're working on a feature where the desired behavior is so well known and immutable that you too will never, ever, under any circumstances need to change it. And the language and platform are absolutes; they too will never change - no new libraries, no change in any of your dependencies; not even a revision tick. You are certain that no one will read it; not even you.
And you can either write it in a terse manner, or a readable manner (but not both). Which is better?
Good code is efficient. Good code is testable. Good code displays an attention to detail. Good code has singular purpose and lacks duplication. Good code is expressive. Good code is written by developers who care. Good code is pleasing to read. Good Code is Clean Code.
Having worked on a system that manages over one hundred thousand purchases per day, I do not believe there are many situations which absolutely mandate performance at the cost of readability. So while I expect the argument, I believe it to be an outlier at best, if not completely fictional.
Given the definition of good code and the likelihood that what we are working on does not require obfuscated code for performance gains, there is no other possible consideration.
Code must be written for readability. If it is not; it is not good code.
Certainly, one can opt to knowingly write bad code, but I cannot comprehend the motive.