One that he can use to intercept Seanchan ships and deal with armies before they ever land. That's usually a powerful advantage even in the time of traveling(when most people can't use the power).

Traveling becomes less effective when we take into account that the Damane can't link and create large gateways, forcing the Seanchan to rely on their fleet for their transport and invasion needs. Seafolk ships will provide fast mobile platforms to repel that invasion, and the most experienced crews to work those ships.

Sure, Rand can wait until the Seanchan approach ports, but the resulting battle could be very dangerous to the surrounding cities, bringing lots of civilian casualties.