What is the significance of performing proper funeral rites?

From: nishita

What is the significance of performing proper funeral rites for dead bodies by burning them as ordained in our vedic scriptures? Does it have any implications on the spirit soul in accepting its next body? Why this is different for different religions of the world for eg: muslims bury dead bodies, parsis abandon it for self-degradation,etc? Does it have the same effect as that mentioned in the vedic literatures?