Most, but not all of the models, do come in 3 levels of detail. Low level was made  to be background objects and to render quickly. High resolution for close-up detail. Medium resolution for everything else. Mind you, these resolutions were determined back when the available RAM on most computers was usually less than 100 megs.

The texture resolutions are not very important as they are mostly small seamless (supposedly) tiles.

I'd rather stay in my lane than lay in my stain!