Yes true, if I understood correctly, I solve in this way, if for example I want to open OWB on a small window, va I want other applications to use the whole window, after storing the window of OWB, i replace the "global.prefs" in the Env-Archive (OWB will later use its Zune config.), done this only OWB will open with al small window, this operation I perform it on all those applications where I want to use a particular resolution, an example on all AmiTube !
I'm trying to pick my brain on what you wrote and believe I have to conclude that there still is some language barrier confusion going on here

If you do open every application on the same screen, no matter the resolution (= width/height dimensions) of that screen then it does not really matter how you organise your open windows. Even stronger, it becomes tiresome to set the window positions and sizes for every different used screen resolution.
That is why having multiple screens is such a bless, as it allows you (for example) for applications that open up a lot of windows or depend on displaying a lot of information to the user to have such application run on its own independent screen (with accompanied resolution/dimensions).
So, for example I can have OWB run on its own screen at a resolution of 1920x1080, while at the same time being able to run my development editor on its own screen with a resolution of 1024x768 and have the workbench run on a screen with a resolution of 800x600.
That way you can have a dedicated resolution for certain programs/applications and be able to switch between them with amiga-M/N.