Competitive pitches for agency new business are messy, expensive and disruptive events.
In general, you should try to avoid them. You can do that by taking a more proactive approach. Have a strategy for targeting the right kinds of clients and nurture the relationship before the account goes up for a formal review.
If you find yourself facing the prospect of a competitive pitch, know what you're getting into.
Treat it like you would an investment. Sometimes you have an appetite for taking a risk; sometimes the potential loss of time, money and morale may not be worth it.