"asdfa"[4..-3] ???
"asdfa"[9 -20] ??
"asdfa"[0..-0] ??
Only seems to make reasoning about code more difficult in return for brevity. Helpful for programmers whose main productivity obstacle is typing speed.
With or without negative indices one can do pointless things with slicing/subseq. Returning an empty string/list is the only sane thing to do in those cases.