For me.. Safety.
Like today when I go into downtown Boston (Rt93 south over the Zakim bridge and into the Big Dig $14mil tunnel) and not having to worry.
Heck even after I left the parking garage, I purposely tooled around a few streets in the financial district just to show off.

hyea:
I went to my second customer, parked in a garage in Cambridge I never been to before... I got yelled at when I went to pay at exit, never to come back again; motocycles not allowed, what BS that was... Of all the garages I park in, they ALL allow me, as long as I pay full car price.