You can do the same in Max, as the UV modifiers have a channel selector with them. I prefer to keep them in the UV space for the simple fact that if I want to create a custom UV map in photoshop, the “Render UVW template… iirc”, only renders what is inside the UV space, nothing outside of it.
I was looking at tessellation and displacement mapping today, and the recommendation from major sources is that you don’t want to use seams in the UV map. You want to separate all of the polygons out, normalize them, and then pad them.
I wish the Unreal Engine (and all the other ones I believe), allowed you to use multiple UV channels, and select what channel you wanted to use for what. In UE4, there could be a setting in the material editor for “Lightmap UV Channel”, and then you could add a variable to tell it what channel you wanted for your Lightmap. The same could be applied for other shader-specific things, like normal maps, displacement, tessellation, etc… Not sure how that would work seeing how I know nothing about shader programming, but it seems like it would be a cool feature to implement.