Thanks. We felt for London commuters just the live image of the map would be enough to enable them to visualise their route. And for tourists/infrequent users the added route planning would show them how and why they should take a particular journey.
You can also manually open and close stations/lines and get instant feedback on how that effects the planned journey (although this is mainly hidden in the UI)
I can't see such a thing anywhere on their website, but in stations TfL often have the inverse; a map showing the closures with the rest greyed out. I've always felt that's the wrong way around.