It is a balance of both.
- Battlefield 2 maps were large and by using this technique the game decreased the number of things that needed to be rendered.
- There are certain maps where it does limit the distance of sight to a certain distance and it therefore limits snipers to that distance as enemies were not rendered past that distance. (If you were pro you could kill enemies beyond that distance)
- Battlefield 1 is not hardware limited in that way but will still make use of the fog as a dynamic weather aspect which serves to render snipers useless at certain distances unless you are pro and can use the fog to hide your scope glint and still workout where the enemy is relative to the 3D spotting.