Why isn't SHIFT+SPACE popularly utilised?
Chrome uses space as "page down", and SHIFT+SPACE as "page up". However, I haven't been able to find a single occurrence of it being utilised during typing.
As a programmer, having it assigned to
underscore (which is often used in variable names to represent spaces) makes sense.
Assigning it to tab for a regular user might even make sense (it's KIND OF an alternative space) which would open up the tab key for a different utility.