When you’re publishing a new model, there’s a checkbox that says “Allow copying” with a little “help” icon to the right. If you click that icon, it tries to take you to http://wiki.roblox.com/index.php/Free_models which immediately redirects to Roblox Creator Documentation, which doesn’t explain the option at all.
I did a search of other posts (in case it was merged into another help page), and it seems like it was simply deleted. It redirects to the main Developer Hub page, and there doesn’t seem to be any other pages explaining the feature.
I think the notice on the web version of this option should be put into the studio option, as it really does a good job of explaining the possible dangers of making the game uncopylocked: