heic

When moving photos from "Photos" to LR on my Mac, LR imports most of them twice. First, a photo identical to what's on my phone and in my Photos app. Second, a photo much larger in physical size is imported also. Where did that bigger picture come from, and which one is the better one? I'd like to know why LR is keeping two formats for the same shot and why one is labeled "heic" while the other is labeled "s.heic". Neither of these seem to be any smaller than JPEGs?