Video Memory

For a regular consumer workload, how much vRAM does the iGPU or dGPU need?
Most (mid to high-end) graphics cards uses GDDR5 instead of DDR3, why is this so,
especially when DDR3 is faster than GDDR5?
(The only dGPU I know uses DDR3 is the Nvidia GeForce GTX950M (2GB DDR3))

vRAM:
https://www.youtube.com/watch?v=Utv144XeHag&ab_channel=NCIXTechTips

DDR3 vs GDDR5:
http://www.techspot.com/community/topics/whats-the-difference-between-ddr3-memory-and-gddr5-memory.186408/

This should have all the answers you need

please gimme some karma too.