Actually catching that you said "new boxes" instead of concepts or topics. Assuming you mean teaching new stuff fast. My coworker tried speed-running onboarding for our software, and half the team missed key shortcuts. Speed can backfire if people don't actually retain it.
Wait, half the team missed basic shortcuts? That's a crazy high number. Speeding through training just means you have to do it all over again later. Real learning needs time to stick.