One advantage to using Kayak versus searching directly with the airlines or some other less limber search portals is that all flights are displayed, including some unconventional booking structures that you might not have been aware of.
One such example is “hacker fares,” which Kayak defines as, “Instead of making you book one round-trip ticket from a single airline, KAYAK plays airfare matchmaker by finding two one-way tickets that together make a round-trip flight. Sometimes that means you might take a different airline home than the one you took to your destination. Other times, it’s the same airline, but they have you in the system as two one-ways.” The company continues, “Either way, you’ll get there and back while usually paying less than you would if it were a regular round-trip flight.”
Interestingly, Kayak also displays ads from Southwest airlines, which is not something that all travel aggregators do. Although not always the cheapest, many fliers swear by Southwest for its liberal change or cancellation policy, as well as giving passengers two checked bags free of charge.