(This is a blog post I’ve had in a "write-me!" folder for years; I am now publishing it in its unfinished form to get it off my mind.)
Programmers are acutely aware of their limited resources: CPU, memory, storage, requests-per-second, screen space, line length, and so on. If programmers are aware of a resource constraint, they conserve on it; sometimes they call this “optimizing.”
Are you aware of a loop? Then you try to “optimize” it, or conserve on it, e.g. by not using a count() in the loop declaration.
Are you aware of the number of lines? You might try to conserve on the number of lines, perhaps by removing blank lines (especially in docblocks).
Are you aware of aware of the size of an array, or the number of objects in the system, and so on? You try to conserve on those, to reduce their number.
But this is sometimes a trap, because you conserve or optimize on a low value
resource you are aware of, at the cost of not conserving on a high-value resource you are not aware of. For example, optimizing a
loop by not using count() in its declaration will have little impact if the loop is
executing queries against an SQL database.
Lesson: conserve on high-value resources that you may not be aware of, not low-value ones that are obvious but of little consequence.