Sorry, I just realised there's no y-axis on that screen grab. Curses!
The graph shows the time (in seconds) spent riding at any given gear size during a 200km brevet. In this case you can see I spent about 4x as long riding at ~70" as ~90".
In fact, I hardly needed gearing higher than 90" (or smaller than 40") at all.
Although it looks semi-continuous if I could remember the block size and chainset on that bike, I suspect the peaks would correspond to gear combinations. If you're using a widely spaced cassette you could probably find the point(s) at which you change at the front and look at whether you're spending a lot of time on either side (i.e. more shifting than would be ideal).
Because there is quite a respectable efficiency gain from having a straight chain, there is some value in working out where you are actually riding in the block (although you could just take a look between your legs from time to time ;-)