The Grove Mega Shield is an extension board for the Arduino Mega for use with the wide range of Grove modules.
Seeed has standardised all the connectors into 4-pin (Signal 1, Signal 2, VCC and GND) 2mm connectors and kept some of the 3-pin (Signal, VCC and GND) 2.54mm headers for Servos, which simplifies the wiring of electronics projects.
The 4-pin buckled connectors also make wiring more stable. The Mega Shield includes Digital 0-21 and Analogue 0-15. Seeed abandons the Digital 22-53 pins for easily installing the Mega Shield with the Xduino Mega/Google ADK.