Lol depends on the show.
Schooling show where I enter literally the day of because we've cancelled a cross country schooling? I'd rather have a reader than look stupid and make a mistake because I just learned the test 10 minutes before in the warm up ring. If it's a recognized show I would never use a reader, but alas I would also be more prepared in general. In the eventing world you can't use a reader, so I've, for the most part, become quite good at memorizing tests (very quickly, if need be).