Is it ever good to keep secrets from your partner?

Is it good to keep certain secrets from your partner to maintain peace in your relationship? Many of us feel that there can be no secrets in a good relationship, but is that view even possible? While most people feel that couples should always be faithful to each other, is it necessary for example,to disclose everything about your past? What about if you feel an attraction to someone who works in your office, but have no intention of acting on it - wouldn't it be disastrous to disclose the fact to your spouse?