To quickly hide your porn
When you look at porn you always should have a site to quickly enter if a parent/roomate enters the room.
If you are a functioning member of society, you may just want to leave the porn up. Because let's face it, Porn is a lot easier to explain than Google+
To prove you're better than everybody else
Chances are if you still use Google+, you're under the impression you are the best person in the world.
To instantly get rejected from any job
Let's be honest. You'd much rather put down that you are a sex offender on the job application than have to put down that you have a Google+ account.
To give people a reason not to talk to you
If somebody at Starbucks sees you on your Google+ account updating your circle, they will most likely consider blowing their heads off before getting involved in a conversation about Google+