Hello 
I wish to put in my game some multiresolutions objects (between 050 meters, per example, my object appear in full resolution, and more then 50 meters, it appear in low resolution)
The solution i find is to do 2 versions of the same object, one in hi rez and other in low rez, i put them in the same place and i put them in specific layers. So i discover today the function Camera.layerCullDistances that is able to set the far clip plane of a layer.
That’s great!!! 
But I just miss an information for it work realy like i would like.
1.I created a script, i copy/paste the script > Unity - Scripting API: Camera.layerCullDistances < in this new script. Then i put this script in the camera of the first person controller, for look if i can make disapear my object after 15 meters. It works perfectly!
2.Now that the object in hi resolution can disapear, i wish to make appear the low resolution after this 15 meters, and for that i need to know how to configure the near clip plane of the layer, on the same way that we can configure the far clip plane in this script
Unfortunately, there isn’t an equivalent to layerCullDistances for the near clipping plane. The only thing I can think of is to have a second camera to render things in the nearground, but I don’t know if that really helps with the optimisation.
Thank you for this precise answer.
I finded other ways for the wanted result, so i explain it shortly for the interrested peeple
the first is to put the low resolution object in a layer, the hi resolution in another. Put some empty at the same place of the object and join to the camera a script that search the distance between the object and the player every 5 seconds, so when the distance is superior then 50 meters, it hide the layer hi rez and show the layer low rez, and if is inferior, it hide the layer lo rez and show the layer hi rez. works fine!!!
the second is to create a trigger that do the same.
i finded a third very interresting optimisation sollution. is to put an invisible cube (shader transparent alpha 0) at the same place then the object hi rez or heavy in polygons. Ten i use in it a sctipt with the command OnVisible and OnInvisible with show and hide layer.
the 4th solution of course is the one in my first post. You can put some litle objects in specific layers that have a camera layer cull distance script and they disapear over the far clip plane defined.
With all this scripts, the difference in the stats view and FPS in incredible!!!