From: Seattle, WA
Agreed. Expectations and negotiations are crucial. Keep in mind that some people's fantasies may crumble in the face of reality.
At present I'm looking forward to a coffee date with someone who owns a few chastity devices, but who only stays locked for a few hours at a time and expects some sort of orgasm by the end of the play session. Since it's open to ruined orgasms and other consequences, I'm fine with this.
If I was going to lock up someone long-term, like a live-in partner, I'd consider what I know of them, their moods and chastity tolerances, and their schedule. If I know that they're going to be meeting up with a difficult person or a situation where their chaste-behavior doesn't serve them well, I may set them loose, so to speak, shortly before that challenge - especially if I'm not going to be around for long enough to take the brunt of their non-chaste attitude.