This is not necessarily true. You would be surprised how many absolutely trivial performance issues can be found in almost every project. Sometimes it's really just about moving computation of a constant value out of a 'for' loop.
I once sped up a program by 90% by turning `new String("foo")` into just `"foo"`. The project was still rotten though, so it ultimately didn't matter.
Your example sounds interesting, could you explain more
Are you familiar with Java? If you use just `"foo"`, then the string will be interned and reused. If you use `new String("foo")`, each call creates a new copy on the heap. This call was inside a very hot loop, thus eating almost all the application's runtime.