I suspect this has already been asked before, so my apologies in advance...
On the web site you can track your training by planning activities in advance (running in my case), and as the days go by, you can mark them as complete.
You can also enter routes by tracing a path on a map and saving the route in My Routes.
So... Why can't you use those routes when planning? In other words, if I know that next Tuesday I want to run "My Favorite 3-Mile Route", why can't I just select that route from a drop-down list rather than manually entering the data? That way, if I review my training history, I know not only how far I ran on a given day, but I also know where I ran. I'd also like to be able to do that when marking a training run as "Completed", so that maybe when planning I just enter 3 miles as the distance, but when marking it as "Completed", I can choose which of my 3-mile routes I chose to run that day. Or if I ran a route that I haven't entered, I can just leave it blank or choose "Other" or something.