What does msfencode BufferRegister option is used for?

[Jordan Trover <shurimaxx () hotmail com>]

I hope the question is not too stupid, but I just started learning masm and I have ported one of the functions from 
syringe.c to masm to execute payloads directly from code. 

All the payloads I tested executed fine but they all crashed the exe that launched them with a memory access violation 
right after finishing executing the payload. So I added a SE handler, but still wasn't able to return to my code after 
the payload execution.

Then I tried encoding the payload, got the same result. But then I tried encoding and using the option 
BufferRegister=EAX, this time the payload throws an exception but I am able to catch it and return.

I read in metasploit website that BufferRegister is "The register that pointers to the encoded payload", but I don't 
fully understand why using that option allow me to catch the exception and without it I can't.

Could someone give me an explanation on the BufferRegister option is involved in the execution of the payload?          

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