Where?
On a home page of a Google-scale website, it is not acceptable. Keep the things as quick as possible.
In a part of an application which is used by one person once a year, it is perfectly acceptable to sacrifice performance in order to gain code readability.
OnIn general, what are the non-functional requirements for the part of the code you're working on? If an action must perform under 900 ms. in a home pagegiven context (machine, load, etc.) 80% of a Google-scale websitethe time, and actually, it is not acceptableperforms under 200 ms. Keep100% of the things as quick as possibletime, sure, make the code more readable even if it might slightly impact the performance. If on the other hand the same action never performed under ten seconds, well, you should rather try to see what's wrong with the performance (or the requirement in the first place).
In a part of an application which is used by one person once a yearAlso, it is perfectly acceptablehow readability improvement will decrease the performance? Often, developers are adapting the behavior close to sacrifice performance in orderpremature optimization: they are afraid to gain codeincrease the readability, believing that it will drastically destroy the performance, while the more readable code will spend a few microseconds more doing the same action.