PCB Antenna design for nRF2401
What is the reason they do this? Is it a more effective antenna, or does it just take up less PCB space?


Both? 

The meandered part is probably an inductive element, increasing the electrical length, and the stub might match the impedance. Looks a bit like an inverted-F antenna.

In fact, it's a meandered inverted F in PCB shape. Probably, you'd call it a MIFA