well I talking from Experience, I found if you have to much your not doing your fs or train sim any good, the more detail slow speed, and you can spoil; it to, as i, ve done in the past, so now when i get home if i cant get it the way it was i,ve got to uninstall FS.
my sf9 and start all over,
But we all learn from are mistakes right!
I don't see how having a lot of planes added to FS9 can hurt performance. Only the plane you've selected gets loaded when you start a flight.
Performance hurted if we demand from our system more detailed textures,planes etc.
In addition ,if we use add-ons for improving these textures its obvious that (depending on our system specs)the system will slow cause it needs more sources to create these textures.
A good and simple example is to set detailed clouds full and create a flight with the weather seted up to Major Thunderstorm or Stormy Weather.In many systems(with add-ons or clean)we will notice the reduce of performance(the crafts are moving like slow motion).