Alliance RTW tickets require you to keep moving in one direction - no backtracking allowed. AirTreks custom tickets have no such rule. You can fly Bangkok to Tokyo, back to Bangkok, then on to Sydney if the routing makes sense for your trip.
Traditional airline alliance RTW tickets (Star Alliance, oneworld) require you to travel in one continuous direction, either eastbound or westbound. No doubling back. If you fly from London to Bangkok, you can't then fly back to Dubai on the same ticket.
AirTreks builds custom tickets that aren't bound by alliance rules, so limited backtracking is sometimes possible. If your dream route requires going from Bangkok to Bali and then back up to Tokyo, we can often make that work. The question is whether it makes financial sense.
Backtracking generally costs more because it adds distance. The most affordable RTW routes move in one general direction, taking advantage of natural hub connections along the way. Every time you double back, you're essentially paying for an extra flight that doesn't advance your overall route.
That said, there are smart ways to handle destinations that don't fall neatly along a directional route. Your consultant might suggest a side trip on a separate low-cost carrier that doesn't affect your main ticket pricing. Or they might find a creative routing that covers your "backtrack" destination without actually backtracking, by connecting through a nearby hub.
The practical advice: give your AirTreks consultant your full wish list, including any destinations that seem geographically awkward. Let us figure out the most cost-effective way to cover them all. Sometimes the answer is a slight backtrack built into the main ticket. Sometimes it's a separate side trip. And sometimes it's reordering your stops so the route flows naturally without any backtracking at all.