I find that when initially exploring a problem space, it's useful to consider functions as “verbs” to help me think through the solution, and that feels useful in helping me figure out a solution to my problem—I've isolated some_operation() into its own function, and it's easy to see at a glance whether or not some_operation() does the specific thing its name claims to do (and if so, how well).
But then after things have solidified somewhat, it's good practice to go back through your code and determine whether those “verbs” ended up being used more than once. Quite often, something that I thought would be repeated enough to justify being its own function, is actually only invoked in one specific place—so I go back and inline these functions as needed.
The less my code looks like a byzantine tangle of function invocations, and the more my code reads like a straightforward list of statements to execute in order, the better it makes me feel, because I know that I'm not unnecessarily hiding complexity, and I can get a better, more concrete feel for what my program's execution looks like.
But then after things have solidified somewhat, it's good practice to go back through your code and determine whether those “verbs” ended up being used more than once. Quite often, something that I thought would be repeated enough to justify being its own function, is actually only invoked in one specific place—so I go back and inline these functions as needed.
The less my code looks like a byzantine tangle of function invocations, and the more my code reads like a straightforward list of statements to execute in order, the better it makes me feel, because I know that I'm not unnecessarily hiding complexity, and I can get a better, more concrete feel for what my program's execution looks like.