As a Roblox developer, it is currently impossible to fine-tune the positioning and scale of randomly generated terrain.
In my case, I want to have a topside to a facility situated in a pretty large snowy terrain area, but cannot use the automatic terrain generation tool because it maps the terrain at the center of the game. This would draw the terrain over the facility that I want to connect to this topside area (which is quite large). I do not want to move the facility itself away from the center of the game, though. I would like to have an option (similar to the Region tool) to scale out a box to mark bounds of the terrain generator, and generate terrain in my selected position and in said bounds. This would help to create terrain in specific spots with specific sizes. Of course you can add a minimum and maximum size for these boxes.
This would be extremely helpful in many cases of development for me, and I think many others as well.
tl;dr - Region tool-like selection box for generating terrain inside