Oh my ! Thanks Mitrail, I red this topic though, but I didn't see this line !
It makes my day !

Well, not really, although this layers are really helpful ! What I was thinking of, is more like : let's say I want to build a rather complicated structure (like a gun rack), involving objects I rotated because i want them fixed on the wall. When I finished, I would like to group it (the rack/support and the guns)into one solid object, so I can rotate it, place it or anything in one piece.
I know I could just select them all and rotate them, but not precisely with the "rotation" field in this selection attribute, because if I do that, it will rotate all my objects independently from the others.
I feel it would improve Eden to have this ability !

But thanks though for your advices !
This new editor is a beauty !

I agree it is possible to rotate them like one solid object, but just with the mouse, not with the "rotation" field in the attributes (even when activated the field), which is a lot more precise and take less time. They will rotate oddly.
But the rotation is not my only point of interest, the ability to group things could be convenient in a lot of situation. It's a kind of relief to group a structure you just spent hours to build. That way you know you won't mess it selecting an element without noticing. Or else.