99.9999% of the time, when I add a new block, I delete the default 20px top margin. I also delete the 30px bottom padding, 200px width and 200px height that sometimes get added to my blocks.
Having an option to configure the default margin/padding/height/widths or at least disable them would be a big quality of life improvement.
I know that one can use the keyboard shortcuts to quickly set the margin to zero, but it's kinda annoying because then there's an unnecessary "margin-top: 0px" rule in the JSON, taking up space. Besides, it would be nicer not to have to do it in the first place.