I forget who I have cut and pasted this for in the past, but if you would really like to be aware of some reasons.... here is what I can come up with. Good Luck with your keeping adventures! 
You can sucessfully keep two corns together, but there is also a lot that can grow wrong. I personally keep most of my corns housed alone, but I do have a few females that sharge a cage while I am making room for them. Honestly though, if I have a certain one that is either very expensive or one of my favorites, I can assure you I won't take the risk. Here are some cons...
1. One or both corns may get stressed out. A beginner keeper may not even notice the signs of a stressed out corn and prolonged stress can lead to illness.
2. It will be nearly impossible to tell who is the culprit if someone regurges or leaves other "clues" to illness in the cage.
3. If the two snakes are not from the same source a quanantine time of at least six months is advised or they can transmit parasites to one another. It is impossible to quarntine if kept together.
4. If the snakes are a sexual pair and not of breeding age, they will breed before the female is physically able to handle the demands of breeding and can very likly lead to fatal complications and perhaps unwanted hatchlings.
5. If it is a sexual pair and they are breeding size, they will breed. Female corns need to be alone while they are gravid, and having another snake in there will only stress out the female during a time where she should be made as content as possible. This also can lead to fatel complications with egg-laying.
6. Lone males put together may fight unexpectedly and suddenly during mating season. One day they may be fine, the other they may be engaged in a battle.
7. I have heard of a few instances that even though the corns were fed separately, when put back together in the same cage one "smelled" the lingering mouse smell on the other and constricted it's cagemate to death.
8. Caniballism in corns is not THAT rare. I've seen hatchlings attempt it in my own home both this year and last.
I am sure there is some I left out, but those are some serious risks to consider before you decide. Oh yeah, I forgot the pros.
1. It saves you a little bit of space.