Many years ago I interviewed at a military contractor. Every time we walked through a work area someone went ahead and announced I was coming through to ensure nobody had something that would require a clearance to see.
...yes? If your secrets are worth an NDA, they're worth a little opsec.
I was responding to a suggestion not to use an NDA, and to 'just share secrets later'. Just pointing out that that's more involved than simply not breaking down (explicitly, in the actual interview) exactly how your middle-out compression algorithm works or whatever.
If they have secrets, yes! Don't give candidates access to secrets.
Yes, again, I was replying to the suggestion that 'oh it's easy no need for NDA, just share the secrets later if they get the job'. Point was it's not just deliberate sharing of secrets you need to avoid in that case. When candidates are asked to sign an NDA, it's probably not because they're going to be explicitly told anything sensitive.