I and more recently my wife have been getting walking directions for short trips by default. It's a nice idea but 100% of the time this has been useless - eg I am running errands and I'm not going to leave the car at store #3 just because I could walk from it too store #4
I can see this be very useful in a foreign city where you're trying to get around and don't know the options.
I love the image of someone in a parking lot with their car being surprised that the walking directions are asking them to leave their car. "Not again!"
More seriously, though, when shopping in roughly the same area of town, the best way to walk is to pick a spot that's close to the last place you're going to shop. It'd be an interesting mapping feature to suggest a spot based on a list of locations.
I can see this be very useful in a foreign city where you're trying to get around and don't know the options.