When we write code, it's essential to consider how human brains will consume it. Fellow programmers will scan over your code, reading the pertinent parts, attempting to gain a running comprehension of its inner workings. Readability is the first hurdle that they must overcome. If they are unable to read and cognitively navigate the code you've written then they'll be less able to use it. This will drastically limit the utility and value of your code.

Programmers, in my experience, don't tend to like thinking of code in terms of aesthetic design, but the best programmers will appreciate that these concepts are intrinsically intertwined. The design of our code in a presentational or visual sense is as vital to its comprehensibility as its architectural design. Design, in the end, is about creating something in a way that optimally delivers a purpose for its users. For our fellow programmers, that purpose is comprehension. And so we must design our code to deliver that purpose.

Machines care purely about specifications and will parse valid code into its parts with little effort. Humans, however, are more complex. We are less capable in areas where machines excel, hence their existence, but we are also skillful in areas where machines may falter. Our highly evolved brains, among their many talents, have become incredibly skilled at spotting patterns and inconsistencies. We rely on difference, or contrast, to focus our attention. If a pattern is not being followed then it creates more work for our brains. For an example of such inconsistency, have a look at this code:

var TheName='James' ;
 var City     =   'London'
var    hobby = 'Photography',job='Programming'

You probably don't enjoy looking at this code. Its messiness is distracting and it appears to follow no particular pattern. The naming and spacing are inconsistent. Our brains struggle with this, and so reading the code, and building a full understanding of it, becomes more cognitively expensive.

We might refactor the preceding code to be more consistent, like so:

var name = 'James';
var city = 'London';
var hobby = 'Photography';
var job = 'Programming';

Here, we've used a single naming pattern and have employed consistent syntax and spacing in every statement.

Alternatively, perhaps we would like to declare all variables within a single var declaration and align the assignment (=) operators so that all values start along the same vertical axis:

var name  = 'James',
    city  = 'London',
    hobby = 'Photography',
    job   = 'Programming';

You'll notice that these different styles are very subjective. Some people prefer one way. Other people prefer another way. And that's okay. I am not stating which approach is superior. Instead, I am pointing out that if we care about writing code for humans, then we should care, first and foremost, about its readability and presentation, and consistency is a key part of that.