The problem people are having I think is that when you have like a car that has not been used a very long time, the foliage starts to creep over it. Fine but then the foliage is connected to something, and a free floating car with foliage sprouting from nothing is rather odd to look at.
Would perhaps then be ok to model some parts of the ground, and exclude it from the total poly and texture count?
The best explanation would be an example;)

