We all want our software apps to perform fast, however sometimes we get so obsessed with immediate performance that we neglect the big picture and actually code in a way that degrades performance in the long run. The problem is that optimizing code for performance usually (1) takes more development resources, and (2) makes that code harder to maintain. About the second point - there is often a tradeoff between performance and maintenance: generalized code is easy to maintain, but because it handles all general cases, it is not optimized for speed. For example, it wastes extra resources on tasks that may not be needed for the current case, but are still included so that the code handles the general case.
So, the trap becomes a developer may spend all their resources upfront trying to optimize a specific component. However, if that component isn't truly performance-critical, then they've: (1) spent their resources on a non-critical item such that they have less resources for the really critical ones, and (2) created a maintenance issue that will continually drain their resources away from the components where a little amount of effort could really optimize it.
What this means is that, in the long-haul, writing maintainable code (which may be slightly slower) will actually yield overall performance gain because you'll continually have move resources to address the real performance problems. Functionality trumps performance - if your code functionally doesn't work, you won't care about performance. So if you're continually being distracted to go and fix bugs in old code because it isn't maintainable, you'll likely shift your mindset from "make this work fast" to "just get it to functionally pass". Of course the trap is that a developer starts out with good intentions - "I was just trying to optimize this code".
The optimal approach is to strike a balance between maintainability and performance. Some practical tips:
Not all code is equal - obviously code that is frequently called needs much more attention that code that is rarely called.
Know what the standard is - Everyone knows that the app should be "fast", but how fast is fast enough? Clichés like "as fast as possible" are what get you into the downward spiral because they encourage you to squander resources on less-important tasks. If you know that given X users, a page should take Y seconds to load, then you can make rational decisions on how to spend your development time wisely.
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