You are telling the site that this set is completely verified, where names are concerned. All names are linked to the correct PID, and remaining cards are checklists and the like that don't have a name to link to. Then the set drops off the list of sets that need to be checked. Eventually, in theory, each sport category would be down to nothing on their lists of sets that need verified. (I think I had either golf or boxing down to zero at one time, but new sets have been added since) If you do it, then notice a mistake, you can still fix the mistake by going to the screen for the individual card. Also, some types of changes to a card in a verified set would cause that set to be moved back to the list of unverified sets. I have no idea if this is useful information to you, but at 2:17 AM it's the best you're probably going to get out of me! I will add that if you do match all the names, and then you DON'T hit Mark As Verified, you are creating extra work for the next person to come along, because they will waste time clicking on finished sets that should be off the list.
I'm going to reevaluate how I collect after the new year. It's just getting way too expensive for the new stuff. Sometimes I just want to buy a pack, not a whole box or even blaster.