Tanks you 
You answer here much of my questionments. I understand the shadows and light deal.
But as DamirH said, and if he did mean that : the Light Propagation Volume (dynamic lighting/GI) is working better for large scale scene right ?
But, i can not use that dynamic lighting/GI with statics and stationary spotlight to produce interior GI ? If in the same time i have a light propagation volume (dynamic) on my directional light ? (i think, only the Enlighten plug-in propose that for now ?)
The Light Propagation Volume manage spotlight (even statics i don’t care, i will see the movable seting later, with raytracing, iam not here) ?
If not, it mean i need to use the lightmass to have some GI in the interior, and deal the outside (my interior is in the middle of 2 mountain surrounded by others mountain, and i need to be able to travel mountain and go in the home) with the lightmass… :s
Whats good is that : lightmass is a precomuting system and doesn’t take any ressources after the computing…
But it’s looking so hard to catch the lightmass method with an interior small room in the same scene than a medium/large environment that i want also to beeing affected by GI to make it real (or any fake GI i don’t care ! :)).
I feel like i need to unify the quantum mecanics with the general relativity 
I think that Enlighten plug-in would be the unifying solution, waiting that Epic Games finish to dev their own dynamic GI in a final version… :s
(and for my bad luck, my english is bad and my understading reading is not that good haha, sorry for that)
PS : different streaming levels is for you some kind of areas instances in a same scene ? That’s look pretty hard to do no ? Need to manage the C++ i think ? XD
PS 2 : for my shadow/light deasapering, it desappear even in a verry small scene, i need to increase the resolution of the shadows, i can not use only stationary light cause they have a number limited (can not use more than 2 close to eachoser).
But…also my directional light shadow’s desappear…(i need to put it in stationay and back in movable to make it come back).