I'm interested to hear from other YC members and alum but when I went through an incubator and we talking about pitches etc talking about total addressable market in this way was really a no no under the idea that it made you look amateur. We were told the best approach and more realistic approach was to start from the bottom up instead of top down.
I think it was one of the reasons that helped us realize what our true potential was and plan accordingly instead of saying we are going after the 100 Billion dollar travel market or whatever.