TFA says the whole codebase is 600k, so that would be 1.8% dead code. IME dead code is much more common in larger codebases as figuring out that code is dead becomes more non-local and changes over time create dead code at a distance. I'm also not sure if the 11k was trivially dead (`if (false) { dead_code(); }`) or if it was more subtle (e.g. dynamically-dispatchable code that can't logically be called).

The 1.8% feels high if it's trivially dead. When I've run simple static analysis on decent codebases before, it's been much lower. For non-trivial dead code, it might be low. E.g. a lot of projects have piles of "dead" code behind ancient feature flags that would never be switched.

A small amount of dead code is fine. E.g. it might not be worth deleting utility methods that you happen to remove the last use of if they are simple and you might re-add a use later. Generated code is often dead since it's not worth specifying to the generator exactly what will be used. Other times, deleting dead code can lead to a valuable cascade of other deletions and simplifications.