It depends. For some people it's their first sample of a player. Whether that's not a truly indicative sample, either way, is case by case.
For example, the first time we/I saw Laczynski was at the showcase post-draft, used in the same role as Cates. He was equally impressive in that role and drew buzz from us and others. I think Laczynski is a better offensive player, but we still had to wait to see what he did at OSU. And he looked even better there. Like Cates, he had strong USHL #s. Now, I had already seen Cates in the USHL ~3 times, so I knew he was this player. We'll see what he looks like at UMD with higher usage eventually (though his usage grew pretty high this week), and if he should go up in our estimation. But at the very least, I think he's the player we saw this week and was underrated by the fanbase before this showcase.
Ginning I'm less certain about. It doesn't have to be all negative, and he did pretty decent. But that's more a case where I still saw his flaws and, again, had seen him a fair share last year. That's where a few scrimmage games doesn't shake my evaluation too much.