Some elements in an environment are more difficult to compute than other elements. Transparency adds to computation time as well as collision detection, not to mention sensors, surface textures, background textures, supplemental processing scripts, and sound distribution. Effectively, the scale of the 'site' is based on complexity. You can ignore the aspects of complexity for a specific application, just as structure, program, codes, and other aspects of design projects are backgrounded in order to focus more clearly on the specific process being investigated. Even as machines and software get faster, these considerations will always be important.
Scale is also a function of movement.
The faster you move through an environment, the smaller the scale of the environment will feel, especially if there are obstacles. Try running through a small house or apartment, even if the spaces are relatively open, the space becomes compressed because you must concentrate on the path ahead. The same applies in virtual environments.