I didn't either, until I learned about compiler command line flags.
But also: the nice thing about conmand line flags is they aren't persisted anywhere (normally). That's good for security.
Typing an extra space should not invoke advanced functionality. Bad design, etc.
This would be really killer if it was always enabled and the same across shells but "some shells support something akin and you have to check if it is actually enabled on the ones that do" is just annoying enough that I probably won't bother adopting this on my local machine even though it sounds convenient as a concept.
YMMV with other shells and base distros