Hey @utkarsh.ayachit, as @Dave_DeMarle said they may seem similar, but serve very different purposes when used together. The env maps needs to be very high res (at least 8k) to look as a background as well, which are very difficult and expensive to find. This feature allows us to use a low res or more generic map to get good lighting into the scene, and then put whatever static 1080p backplate we want into the scene as the background.
This was a key feature that my company paid to have implemented as part of our recent contract with Kitware, and we now use it all of the time. PLEASE do not remove it.
I would not be totally apposed to rearranging the functionality to make it clearer, but as Dave will remember there were quite a bit of issues getting this to work correctly so I ask that you verify the updated functionality with either Dave, @aron.helser, or I.
Please let me know if you have questions, thanks.