This is the aero-glitch. the game-physics are always calculating the drag of the block at the forefront. When you make this block detachable you will have zero drag on the block behind.
Especially on big creations with high drag this is making sense, because you can save a lot of necessary power and weight and still go relatively fast. The transparent color is only that it does not look that bad...You will find many builds on workshops where this is used.

I've got a question why are there so many detachable blocks with so many clear blocks?

Very nice to hear that you like it , because it always takes much time to create and tweak his complex builds.

one of my personal favs

Great plane