Secrets come in many forms . . . some secrets - - - like your friend confessing her first kiss or the plans for your nephew's surprise party are serious business. Little drops of trust that build an ocean that is a relationship.
Other secrets, like a co-workers negotiations with a potential new employer or your bosses plans to retire, are important because someday you may need the favour returned.
I come from a family where "secrets" are few and far between. We all pretty much lay everything out on the table and deal with it. It works for us.
My main thought to guide what secrets are meant to be kept is simple: Does keeping this secret put anyone in harm's way? Telling about harmful behaviour -- either harm of another or self harm is necessary. It can save a life.