You get better hop utilization, you can brew all grain if you choose to, some say you don't get an extract twang. FWIW Zainashef mentions full boils being a key to making great beer, along with pitching the right amount of healthy yeast.
Very big con: You're going to want a wort chiller.
If you save $50 by not getting a 5 gallon pot with the kit you can get an 8 gallon pot from Amazon for about that much. It'd just be a part of your system that you didn't need to upgrade if you decided to fall further down the homebrewing slope. You can always do a partial boil in an 8 gallon pot, you can't do a full boil in a 5 gallon pot. You can make good homebrew so many ways though, tons of people make great homebrew doing partial boils including my pal Jamie who's beers I'm always jealous of
