Mourningfrost builds

Hi. I saw some builds, with hight dex, and Mourningfrost boots.
These builds have more hundred cold, and physical resistances, but tons of lightning resistance.
How this work ? I not found anything on this builds to take the cold damage as lightning example.
Am I blind ? Or these build really use this huge minus resistances from cold and phys ?

Which builds are you talking about? Because they may have other interactions somewhere

Example, some rogue falconer builds.

Mouningfrost boots adds flat cold damage per point of dexterity but reduces cold and physical resistance. Any build using Mourningfrost with 100 or more Dex will need %175 cold and physical to remain capped.

What makes the boots good is that any spell or ability that has high flat damage percent added scales really well with the flat cold damage. Shadow daggers have %400 added damage effectiveness so they are a popular choice with the boots.