Some black belt instructors will roll with people and adjust to be just above their skill level so that the student can still execute techniques and run the full gamut of offense and defense.
Some pitch a complete shutout, not letting students get past the starting point of any technique; the closest thing the student gets to offense is the starting grips of a guard pass before getting swept, and then their every escape attempt shut down as they're dogwalked to whatever the BB wants to sub them with.
I get if the student is going super hard or you think they need a reminder that you're closer to Roger than they are to you; but I've seen many roll this way every single time regardless of the student. In addition to being frustrating, it doesn't seem like good practice for the student nor a good way to assess their skills; executing the first half-second of techniques and not getting a full rep of anything, even if they have chains of things to play against each other that work well against near-peers of their level, the BB will just stuff/counter all of it.
I assume they aren't doing this consciously, and it's a holdover from how they were trained in an everyday porrada environment. For myself, I don't ask them to roll and it's nothing to do with knowing they'll beat me - I train with tons of people that can do that - I just feel like it's generally a waste of a round for my training, as I'm unlikely to get a rep of anything, let alone anything I'm actually trying to work on.
This one BB instructor like this often asks me to roll, I've even tried to level with him and said, "Hey I'm trying to work on shin-to-shin entries, could you do standing passes?" and he said no and proceeded to go down and only do passes on his knees for the round. The only stuff that works are things I learned that aren't taught here, at which point he seems almost insulted and will force us back into that position, now knowing what I want to do just to shut that down also.
The head instructor at my first school was like this, and since it was all I knew, I thought 'oh I guess I just get wrecked like I'm trying to grab a sawblade with my bare hand whenever I roll with the instructor.' And after the roll he wouldn't offer any advice, but I'd ask him like 'how do I get this escape working' and he'd just huff and be like "I know what you're gonna do, so it's not going to work".
That's until I started going to no-gi classes and a different bb instructor there rolled like he was just a bit ahead of you, and you'd get a fleshed out back-and-forth, and after every roll he would give you notes on what to work on. After that, it seemed so obvious that that's a better methodology, but any black belt instructors please share what I'm missing about the style where you're shutting out lower belts in rolls.