I think Mike brings up a great point that the audience is important to consider. I’ve never gone to a competitor, in that case I would definitely be more restrictive. If you know your company likes to keep things around and potentially release them then I would also be more restrictive. I have had someone come in with cancelled projects and show them, and not leave them. In that case the projects had been cancelled a couple of years prior and the company in question was starting to fold and everyone knew it, so the potential for them to use the project was low. I thought the way he handled it was professional and it didn’t raise any red flags.
As someone who is a design leader I try to empathize with my team here and when something is canceled and totally dead I give them permission to show it in their personal portfolios. Portfolios are different then they were 10-20 years ago. Yo used to only put a portfolio together when you were interviewing. Now people keep their portfolios continuously updated online, so the times are just different.