I thought later on you would exchange OTHER blocks made with modelling 3D and mania script ... ?

I heard that when custom blocks will be enabled, it would be saved in the GBX file when used in a track.

Macroblocks are pretty handy when it comes to scenery...
You can make a building, save it and place it again and again and again and again...
Or if you make your own campaign for instance, you maybe WANT to repeat some elements from track to track... I pretty much like this feature...