Caveat: I am retired. Programming was a major part of my career between 1995 and 2005 but I mostly do HTML/CSS these days, with only enough PHP to glue others' existing scripts together.
What I determined back in the day is that efficient coding is unnecessary for performance when the wetware BKAC would always be the primary limiter on speed. Since virtually all of my work was repurposing documents from old versions of Word, Excel, WordPerfect, Lotus1-2-3, and other outdated apps to newer standards (mostly early HTML), I did not have to worry about shaving off microseconds. The typing speed of the person selecting the raw data had more impact on performance than the programming. So I was much more concerned with whether I would be able to rewrite a handler for a Windows3.11 app to work on a Windows98 version, if that need arose.
If I had been working in an environment where microseconds counted, I would have used a compiled language and a different approach.
My old-timer's advice to you young'uns: Look at the environment you are coding in and match your coding style to fit its shape. Eschew becoming the cleverest code monkey in the cube farm and focus instead on becoming wiser than all the others.