Threats are external to your agency. They might come in the form of a new competitor, a bad national economy or conditions that are completely local to your community. A terrorist attack anywhere in the world would be a threat as it might keep people from traveling.
Why is it better to have a travel agent?
Because travel agents are often working with airlines, hotels, cruises, tour companies, and more on multiple clients over multiple years, they're able to negotiate better deals and access better discounts than you'd be able to on your own. Think of it as bulk buying.