Cons:
sharing of illnesses leading to higher vet bill and/or death of both rather than one
creates competition for hides
may cause stress leading to illness or going off feed
they're not social creatures (not really a con just a fact)
how can you monitor feces if you don't know who it belongs to?
Pros:
None for the snake, but for the owner may initially be less expensive regarding housing - but that can be changed by increased vet bills, etc.
Some of made it work, although I've yet to hear any success with it over the long run. Not worth the risk to me as I believe it my responsibility to provide the best care with my snakes well being (not my wallet or limitations on space) of utmost importance.
Just my opinion. 
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Check Out My Albums
1.0 Ball Python "Aragorn"
1.0 Kenyan Sand Boa "Gimli"
1.0 Saharan Sand Boa "Frodo"
0.1 Rough-Scale Sand Boa "Arwen"
0.1 California Kingsnake "Gentoo"
1.0 Mexican Black Kingsnake "Indigo"
1.0 Snow Corn snake "Chile"
0.1 Australian Cattle Dog/Pointer
"Kira"