Being broke is a huge distraction to most founders, having to focus on the distractions of family, sometimes a spouse and/or kids, and struggling to pay bills - none of that is a good thing for one's ability to focus on getting your startup to any kind of critical mass.
Un-fun things startups do when broke: Digging through your belongings for spare change to buy a meal while you're working on closing a deal is not fun. Closing your 401k is not fun. Trading in your car for an ancient beater is not fun. Keeping a straight face with clients while screaming inside is not fun. Staring at an empty cupboard wondering what you're going to eat is not fun. Coding on an empty stomach is not fun. Selling your furniture is not fun.
If an important deal gets delayed (which it always does), and you're living broke (AKA ramen profitable) to keep as much as possible in your business, you may have to do all the above and more to get through lean times. Far better to avoid the distraction of fighting to survive by not being broke.