I have a problem with it when it costs us football games. You want to ask two veterans to compete for a job, fine with me. You want to ask two rookies to compete for a job, fine with me. But when you pit a rookie vs. a vet, it's not really a fair competition. The veteran doesn't have to learn the playbook and the scheme. Of course, that begs the question: "Do you always start a rookie over a vet?" No. You have to assess if the rookie will quickly become the better player with reps and whether the rookie is ready to play.
Now, some will retort that Goff isn't ready to play. I don't agree. Watching Keenum out there against San Francisco, I have no doubt in my mind that Goff will quickly become the better player with reps.(if he's not already the better player, which I think he likely is)