On The Goldberg's, Dave Kim was originally only supposed to appear in one episode, where Adam wanted hos friends to join him on a Goonies-like adventure and only invited Dave Kim to be Data. It's mentioned that Adam never invited him over before and the real home movie scene at the end shows that the real Adam and Dave Kim only hung out once.
After the first season, Dave Kim started appearing regularly, even appearing at Adam's house a lot. And yet I feel like Dave Kim has appeared more often than Adam's other friends, both at the Goldberg household and away from the house. It especially seems like it for the last two seasons.
And this might be a case of "charicterization marches on", but in his first appearance, he seems like the only sane man in Adam's group of friends (though you could hardly call him a friend then... though Adam did invite him over along with his other friends later in the episode, when he needed them for a real treasure hunt without trying to make it like a movie, and for some reason Barry later invited him over to get his opinions on a video of him that Adam recorded), but when he became a regular, it seems like he's become the weird friend among Adam's friends. Actually, he seems part-weird, part-overconfident.
And something that might be better for the "what's the deal...?" thread: It's often said that Emmy Mirsky is Adam's best friend, but I feel Chad Kremp makes for a better best friend, since they both like making movies. It actually seems like Chad's mother appears more often than Chad does. Though in the episode Agassi, which had some focus on their friendship/drifting apart, Chad is referred to as Adam's best friend at one point. And Adam often does refer to Pops as his best friend almost as often as Mirsky. But I feel it's weird that Adam and Emmy Mirsky are best friends, as she doesn't seem to be too happy when she is around Adam. She often gives the kind of facial expressions that seem to give that impression (though it could be typical teenage girl expressions), she often seems to insult him and be uninterested in things they do, many episodes focusing on her seem to involve some conflict between the two, she also didn't seem to want to be part of Adam's Goonies adventure (and when Adam gave a well-meaning comment on her being like a dude to her, she gave a comment about Adam being like a girl which seemed to be more of a genuine insult, though Adam seemed to ignore it).