I live with my cat. No one else, just the two of us. I love it. However, there are some drawbacks.
Pro: You don't have to clean. Your mess is your mess. You clean it up when it's convenient. If your favorite pan is dirty, you have no one to blame but yourself. You can leave your dirty clothes laying all over the house (because we all strip naked in our kitchens from time to time, right?)
Con: You don't have to clean. The freedom to not pick up after yourself is a cruel, cruel trap. It takes a lot more motivation to clean when your place is trashed. Also, you can't have company over without apologizing.
Pro: You have a lot more privacy. Remember that thing I said about stripping naked in the kitchen from time to time? You can't do that with a roommate (at least a platonic one, unless you're really really close). Heck, you can exercise naked. You can even talk on the phone about anyone without worrying that your roommate is overhearing and repeating later.
Con: It's harder to have a social life. If you don't leave your house, you aren't going to see anyone that day. And unless your friends lives across the street/down the hall, you have to plan a lot more. No more spontaneous dinners out, or a spur of the moment decision to go to for a walk with them. It takes some effort to coordinate things. Despite how Friends made things look, no one leaves their apartment unlocked while they're not home. Nor will your broke friends constantly hang out in the same coffee shop every day. That shit's expensive.
Pro: You can definitely be inconsiderate. Unless you have neighbors in the same building, you can play music, watch TV, exercise, dance, cook, etc at all hours of the day. Get up at 6 and feel like turning up the metal and doing jumping jacks? You can. Want to make curry at midnight while watching your favorite Bollywood movie? If you can stay awake til 4am, go for it. Who is going to tell you "no"? No one. Because you live by yourself, and as long as there is food in the bowl and no crap in the litter box, your cat won't care what shenanigans you get up to.
Con: You don't have to stick to a normal person routine. While watching Shahrukh Khan make a puppydog face a woman half his age while singing and dancing at 3 am may be really fun, it is definitely not a normal thing to do. Being asleep at 3 am is a normal thing to do. Granted, having a roommate can keep you awake sometimes ("Is she still on the phone? It is 3 am!"), turning off the noise and light so they can get up for work in the morning will also help you get up for work in the morning.
Pro: You don't have to compromise. Yeah, it may be there turn to call the landlord about a repair, but you really want it done now. That picture of that turtle may creep you out, but your beloved yet ugly painting of a tree is across the room from it. Yes, you do most of the cooking, but their food deserves a cabinet too. You think he just needs to put on a hoodie, but having the heat at 55 in January in Minnesota isn't something most people are used to, you guess. Reasonable, but really?
Con: There's no pressure to get stuff done. Yeah, the hot water isn't hot enough, but I can live with that. I should probably hang up the painting of a tree, but it's just me, and I don't really need it up. Yeah, I should probably clean the bathroom, but I'm ok with cat hair on the floor.
Overall, I'm bossy and inconsiderate and anti-social and bachelorish (yeah, it's a word now) enough where I prefer to live alone. Despite the fact that I am terrible at cleaning, exercise mostly nude, play my music at odd hours, and have trouble going to bed sometimes, I think it suits me better than having roommates.