Render Element Calculation

can i get more info on how Vray Engine do calculation, if i add multiple render elements on single render layer ?
it is simultaneous process or one after another ?
i think if process is one by one then it will be time consuming process bcz loading whole scene for every render elements separately will take
Time/ Memory / burden on hardware.

Thank you

If you have render elements they will be calculated in parallel to the main pass. So the scene will be rendered just once.