You can search for the full science behind it, but metal cans that have a breaching dent will allow air and bacteria into the can. Plastic liners make it very u

You can search for the full science behind it, but metal cans that have a breaching dent will allow air and bacteria into the can. Plastic liners make it very unlikely for small dents to actually cause a breach, whereas with old “naked” cans that was not the case. Cans with deep dents are not protected however, and these should always be discarded.