We can say that writing code for humans is broadly about the clarity of intent. And writing code for machines is broadly about functionality. These needs do cross over, of course, but it's vital to discern the difference. We can see the difference if we were writing code only for the machine, focusing purely on function, and forgetting the human audience. Here's an example:

function chb(d,m,y) {
  return new Date(y,m-1,d)-new Date / 6e4 * 70;
}

Do you understand what this code is doing? You may be able to decipher what's going on in this code, but it is intent—its true meaning—will be almost impossible to discern.

If we clearly express our intent then the preceding code would look something like this:

const AVG_HEART_RATE_PER_MILLISECOND = 70 / 60000;

function calculateHeartBeatsSinceBirth(birthDay, birthMonth, birthYear) {

 const birthMonthIndex = birthMonth - 1;
 const birthDate = new Date(birthYear, birthMonthIndex, birthDay);
 const currentDate = new Date();

 return (currentDate - birthDate) / AVG_HEART_RATE_PER_MILLISECOND;

}

From the preceding code, we can discern that this function is intended to calculate the number of times a heart has beaten since birth. There is no functional difference between these two pieces of code. However, the latter code better communicates the programmer's intentions, and thus is easier to understand and to maintain.

The code we write is primarily for people. You may be building a brochure website, programming a web application, or crafting a complex utility function for a framework. All of these things are for people: people who are the end users of GUIs driven by our code or people who are the programmers making use of our abstractions and interfaces. Programmers are in the business of helping these people.

Even if you're writing code only for yourself, with no possibility of it being used in any way by anyone else, your future self will thank you if you write clear code.