Personally, when we first started really getting into wine and exploring, buying lots of different producers and drinking new things frequently is also about the time we discovered CT, because our collection got unwieldily to maintain without a database. I also started rating regularly, mostly for my own edification. Basically for the purpose of: Is this a wine I want to buy more of?
Now that we’ve settled into a wine rut (happily) and established relationships with wineries that we buy from regularly, etc. I find myself rating far less frequently. It’s not that we never try new things, because we do, it’s just that a large portion of our monthly/yearly consumption is now made up of tried and true favorites; makers/labels we love that are in our price range and we buy regularly. If there’s something particularly spectacular, or surprisingly disappointing, I note it, but otherwise, it’s more, ‘Yep, that’s what we expected,’ enjoyment that I don’t feel the need to rate.
As for score clustering, I think that’s logical. I mean, we buy wine we expect to enjoy, and usually we do enjoy it. Some more than others, but as we gain in knowledge and experience, separation gets smaller because we sample less wine we don’t like. I tend to score --again, almost entirely for my own use – on a grade-like scale. Like, 86 and below are B- wines; not really what we’re hoping for (these are fairly rare now). 87-89 are "B"s; fine, but probably wouldn’t buy again. 90-92 “A”, good to very good and 93-95 is “A+” excellent. That allows me to go back and refresh my memory when I’m thinking about getting more. Do I really need this? 89 is probably a no, while 92 is a definite yes.
I’m not trying to be an influencer of anyone other than myself since, like most here, I already have more wine than anyone could ever even conceivably, “need,” and I’m usually trying to talk myself out of, not into, purchasing more.