Where the GAI hallucinates an api it is not always easy to find out if it exists given different versions and libraries for a given task, it can easily waste 10 mins trying to find the promised api, particularly when search results also include generated ai answers.

Also there are plenty of mistakes that will compile and give subtle errors, particularly in dynamic languages and those which allow implicit coercion. Javascript comes to mind. The code can easily be runnable but wrong as well (or worse inconsistent and confusing) and this does happen in practice.