I presently work in a canning/labeling factory. Yah, it sucks, but it's a tween job to pay the piper since my old boss decided to stay drunk and hide out in the islands with his bar bride. We have meetings weekly on dented cans. Yes a dent does indeed indicate a possible breech of the can's inner lining. We study this chit to no end. Once the inner lining is breeched you have a situation of the can's contents in direct contact with steel. Yup, just simple steel. The contents, almost always include water, brine of water, salt, sugar, etc. Steel and these substances do not play well together. Our rule is "If it's not a perfect can, it's trash". This company's trash bill is $12,000 per month, if that indicates the volume of what we toss.
As an aside, the slightly dented cans are offered for employee sale at an incredibly low price (about $3.00 per case). I buy none.