We've found that even the smallest of improvements can make a big effect - especially on low-powered devices.
So, for instance, we populate a select box with a list of addresses for the user to pick from.
Instead of looping through and appending each address as a select option, we now append a single string containing all of those options - so a single DOM manipulation instead of 50.
It's these types of changes that give us a 10ms or so boost which can be the difference between passing and failing CWV, and more importantly, giving our users a better experience.
Adam