I would say that if your game needs a fast travel option (as in "let me go instantaneously to point B), it's a clear indication that your map is too big.
It litteraly means that, after a while, the player doesn't want/doesn't see the point to play your game outside of some key areas..
In
LA Noire, I drove once or twice and then let my buddy do the job for me because there was NOTHING to do between missions.
In
RDR, I forced myself because the landscape was amazing

. Other than that it was booooring.
On the other hand,
Batman Arkham City's map was big (not huge) and provided an actually FUN way to go from A to B. Flying was so smooth and fun that the feature alone made it something that I wanted to experience again and again.
The same goes for
Zelda SS : Going to the opposite point of the map was fun because the world is well designed and fun to explore. Plus, you could always quickly fly there. The only complaint I have is that the transition was not smooth and broke the feeling of a real open world..
And in the middle of this there is
SoTC : A huge and empty map with next to nothing to do but that the player want to explore. it's so...beatifully eerie (and the means of transport is fun !).
So yeah, you should always design an interesting and fun map in which the player will want to move into at any time AND/OR design a way to travel that is faster and fun but that will let the player actually enjoy your big map and feels that he is a part of it.