Newbie question about decklink

Forum and google search only yielded vague and confusing results so I'll ask here. I'm probably jumping in way over my head even worrying about this at this stage (I'm extremely new to video editing). I'm seeking to learn DR so I can create short product videos for my side business. Nothing major. But I keep seeing ads and posts about decklink and I can't figure out what it's for.
Blackmagic site states, "DeckLink cards let you capture from cameras, decks and live feeds directly into editing". So does this mean it simply bypasses me having to remove sd card from camera, insert into PC, and drag and drop file into File Explorer so I can open in DR? Other articles talk about video quality. I was under the impression that vid quality was governed by the camera used. Am I losing data/quality by manually transferring file from sd card to PC? I'm confused.
Blackmagic site states, "DeckLink cards let you capture from cameras, decks and live feeds directly into editing". So does this mean it simply bypasses me having to remove sd card from camera, insert into PC, and drag and drop file into File Explorer so I can open in DR? Other articles talk about video quality. I was under the impression that vid quality was governed by the camera used. Am I losing data/quality by manually transferring file from sd card to PC? I'm confused.