Circumstance forced me to do so very early into a relationship. It was incredibly challenging and stressful, and looking back it's amazing that it worked out the way it did. When you don't have money for food and you're living out of a back-pack in public spaces, it's kinda hard not to accept an offer for a roof over your head. With debt payments taking up every pay-check, I didn't have many other options. It definitely made us stronger, but there is also the incentive for commitment that we realized we had after a couple of months. If we made it through everything that life threw at us, I don't have any reservations for the future. I think it only worked though because of the type of people we are, and the relationship that we developed very early on. Once I was able to get out from debt and actually pay for things it took even more stress out of the situation. The idea of living together became the accepted norm. It's weird not living together. That's the hardest part; after doing it for almost a year, moving out (again, due to circumstance) was very hard to do. I'm currently living back in the parent's house due to the inflated costs of grad-school tuition, but in nine months when it's done we're moving back in together for sure. I wouldn't have done it any other way.
TL;DR
I wouldn't recommend it early in a relationship, but sometimes it works marvelously for the individuals involved as long as there is open communication and each has their needs being met.