GB - the point leroy11 rightly makes is that often I don't have the reservations when I buy the ticket, and frankly I don't necessarily know where I will transit or stopover. So in principle leroy11 is right. As I commented in another thread, if you know that in any case you are going to have to reroute your ticket, and if you are buying it open-dated, and, as we know, you generally do not get charged for changes in taxes when you reroute, then you may be able to save a considerable sum of money by buying your RTW tickets with just a minimum number of (low tax) segments and then reroute later adding all the other segments.

So the point is valid, but frankly it has always seemed like a bit much hassle to me to optimise the tax strategy.