I always crack a card I picked up for a set build no matter the grade or cost. I want it in it's proper place in the binder. I do have a couple dozen or so cards I've kept in their cases. Those are generally cards that I've spent a lot of time/money on, things that appear to be delicate that I want to protect or odd shaped items that would be hard to put in a binder page. I don't care about the grade or value, I just don't want to damage them in handling. A couple of examples from my Billy Pierce collection:
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