It depends a bit on context... and scale of scale.

At my first software engineering role the system I 'inherited' (The guy who wrote it quit after it launched, I was hired on after) was only used by 5-10 users at a time. On the flipside, one or two of those users would do things that the system was advertised as being able to do, but would really stress out the system and slow certain operations down for everyone, including exposing our company to financial penalty risks. We actually for a time slowed down trying to get large customers signed up, because even the business folks had to manage enough complaints that they didn't want to risk damage to our reputation. [0]

At my second job, well, I remember the debate I had with the manager about a change I suggested to improve memory allocation on a new email templating process he wrote. He then gave me a lecture about 'premature optimization'. Then when the thing kept crashing with OOM errors he cribbed the parts of my changes that solved the memory leak but left out the pooled buffer to save face. [1]

[0] - The thing was written such that we could only process 2 messages concurrently from a given integration partner at a time, we eventually fixed it by moving the processing to actors behind a consistent hash router.

[1] - The pooled buffer changes were 5-10 extra lines total, lol.