The serrated bits are probably intended for cutting through fibrous material (eg: ropes, tree roots), just like the teeth on your trusty bread knife.
However, the design is so conservative that they don't actually seem to be very useful in this role. This may be due to concerns over being "humane" to enemies (saw-edge bayonets not PC) or simply because whichever Civil Servant approved the design didn't have a clue what he was doing (more likely).
By the way, the horizontal groove in many bayonets (called a "fuller") is not intended to encourage blood flow or to eliminated "sucking" sounds when you stick it in someone.
The fuller is just there to reduce weight a little without compromising rigidity.