Also a lot of people are doing RTWs on a constant basis.
In that case you have to get to your starting point only once - then keep circling the planet.....
RTWs are very flexible (except getting to from the starting point). So you can change the routing (for a fee) or dates (free). Ideal for a lot of people who travel a lot. I know some people who have 3 or 4 RTWs open at the same time.