I have blogged in the past regarding the rendering settings in X-Plane, but this seems to come up periodically, so here we go again. Invariably someone asks the question: "what computer do I have to buy to run X-Plane with all of the sliders set to maximum?"
I now have an answer, in the form of a question: "How hungry do you have to be to clean your plate at an all-you-can-eat buffet?"
There is no amount of hungry that will ever be enough to eat all of the food at an all you can eat buffet - you can always ask for more. And when it comes to rendering settings and global scenery, X-Plane is (whenever possible) the same way. You can always set more traffic, more birds, more objects, more FSAA.
Now the all-you-can-eat buffet doesn't have infinite amounts of food in the building - just enough that they know that they won't run out. And X-Plane is the same way. There is a maximum if you set everything all the way up, but we try to make sure that no one is going to hit a point where they want more eye candy but they've maxed out the settings. Eat all you want, we've got more.
Why on earth would we set up X-Plane like this? The answer is choice.
If you go to an all you can eat buffet, you can fill up on nothing but potatos, or you can have five pieces of chicken. It's up to you. X-Plane is the same way - you decide if you want objects to be visible farther away or more densely. Would you rather have roads or trees? Birds or high frame-rate? You decide!
Not everyone's appetite is the same, and not everyone's taste is the same. This is very true when it comes to flight simulation. There are huge variations in hardware capability, target framerate (some users don't mind 20 fps, some demand 80 fps) and in what part of the visual experience people care about most (objects vs. FSAA vs. visibility distance, etc).
Given such a heterogeneous environment, the only way to meet the needs of a wide group of users is to present choice, and make sure that we have enough of everything.
So when you go to set the rendering settings, don't think that setting objects to anything less than maximum is like only eating half the steak you bought at a steak-house. Rather, the rendering settings are like picking which food from the buffet makes it to your plate. You choose how much you want based on what you can consume, and you pick and choose what is most desirable to you. And like an all you can eat buffet, don't eat too much - the results won't be pleasant!