I'd like to add that although a symmetrical natural fly (+1/-2/+1) has risk on both the upside and downside, there's a distinction one should be aware of.
Example: 105/110/115 call fly. If spot closes below 105, the entire call fly will expire worthless, obliterating your debit. But if spot closes above 115, you potentially have assignment risk, which is why its prudent to manage butterflies. So while yes theres risk on both sides, theres a different type of risk on the upside compared to the downside.
Hope this helps.
But if you left it unmanaged and closes above 115, you end up flat anyway right? (just losing the debit if it was initiated as a sym. natural per your example).
The real assignment risk is if spot closes between 115 and 105.
Please correct me if am wrong, sometimes I get such a hard time closing them that i'm exploring the what-ifs in letting some of them expire.