Sometimes you feel like an accelerator table, sometimes you don't.
Letting in the riffraff.
What happens if you use it anyway?
Does it have a special under-the-table deal with the Unicode Consortium?
Some retro-reverse-engineering and the weird micro-optimizations.
In case of emergency, go look for something else.
For backward compatibility with pre-standard C.
A bit too much search/replace during porting.
Ways of dealing with the fractured address space.
It depends on the language projection.