Open Meshes vs Closed Meshes

Good morning everyone!
I was creating a level in blender when a doubt arose and I hope that some of you can answer my questions. is there any difference in rendering open mesh and closed mesh? I am developing a mobile game using the URP with real time lighting. Removing the faces that are never rendered by the camera (for example the base of a rock in contact with the floor) the polygon count drops. is this the best way to optimize a scene and reduce the polygon count or shouldn't I worry? Thank you in advance

 

Getting rid of polygons (specially if they're never going to be seen) is always a good thing for performance and memory.

It is worth the effort? well, it depends on how much impact poly count has on your game's performance, and how much work you save by not removing unnecessary faces.

 

Thankyou very much for your answer. i think i will go for a poly reduction it will takes a little but on mobile is better to go for full performance!