[pjc50]

It keeps the code closer to the left. It also keeps it conceptually simpler if you can discard a bunch of "obvious" cases early on.

[jakelazaroff]

Yup, this is my exact rationale for preferring this too. Branches are a significant source of complexity and early returns are one way to tame it — have the “meat” of the function deal with as few invariants as possible.