Pros:

-Totally free to do whatever you want to, all the time
-Get to wear whatever you want
-Can go crazy with hair/make-up 
-You have way better friends than people in relationships
-You can play loud music and dance around your apartment naked while eating a stack of cheezits and poppin your zits. No judgement. 
-No fighting/constant drama with your SO
-Happier if you are a woman, statistically 
-No one else to mess up your life/apartment
-Get to have better relationships with yourself, your family and your friends
-Flirting
-Awesome first dates
-You can move to a new city anytime you want!
-Probably better at your job
-No pressure to have kids 

Cons:

-identify with Carrie Bradshaw :(
-Boring family members have nothing else to talk to you about than whether you have a relationship.
-Bad first dates 
-More depressed, if you are a man, statistically 
-Might be forever alone :(