One theory on XLAT is that it's there to make it easier to adapt code originally written for 6502, where the "indirect indexed" addressing mode was popular. The

One theory on XLAT is that it's there to make it easier to adapt code originally written for 6502, where the "indirect indexed" addressing mode was popular. The zero-extended 8 + 16 addition is the same, and this would otherwise require a sequence. For example, to do code page translation on 6502 you'd definitely use indirect indexed at the core. But yeah, this is an oddball instruction, one of the most non-RISC-like in the set.