What kind of perks am I entitled to with a London Day Travelcard?

London Day TravelCards can’t be booked independently, but will be offered as an add-on to any journey that terminates at a London station. Travelcards are valid for travel on:
the Tube, Docklands Light Railway and buses
trams, where your Travelcard includes Zone 3, 4, 5 or 6
National Rail, excluding Heathrow Connect between Hayes & Harlington and Heathrow, and on Heathrow Express
Scheduled Riverboat services, at 1/3 off the normal fare. Just show your Travelcard (or Oyster card with a Travelcard on it) at the time of travel

Please note: your Travelcard must be valid for all the zones through which you are travelling.
Trains to Heathrow Airport go to terminals 1, 2, 3, 4 and 5. The approximate journey times are 15 minutes to terminals 1, 2 and 3 and 25 minutes to terminal 4.