i would say i mostly "free" roll. My goal changes with each position.
When i first started out i would focus on specific aspects on my game. But i don't really "focus" anymore.
As a white belt I felt like I progressed the most when I was drilling things that I didn't have a good handle on. Mainly working off my back in guard. It was so foreign to me, I had to drill everything multiple times until I got used to it. Now it's mostly just an equal balance between the two, with me drilling something that I don't feel I quite grasped during the time that the instructor was teaching it.
When I'm free rolling, it depends totally on who I'm rolling with. If it's a somebody better, somebody less experienced, somebody far bigger, somebody far smaller, etc, I'll work on whatever suits the situation.
I don't think people should tell their rolling partners that they are going to do something,
Example, recently I've been working on a sweep, I just try and use it every single time I have him in Open, close, spider guard...