when in doubt...muck
When is it benefical to show your hands to your opponents? What are the cons and pros?
My opinion is that beginners/intermediate players should ALWAYS muck. I've been playing live for...ugh... 30 or so years and online for about 14 or 15. It's almost always never a good idea to give free information. That being said, I played a live tournament last week where I showed a couple times with specific purpose. Unless you are really experienced and understand your table image and grasp how you are altering or controlling it, I just never ever show.
In this case, I had the chip leader on my immediate right. He, and the next 2 players were very soft in protecting their blinds, and I wanted to keep it that way, so I showed a couple of big hands I raised with to give the impressions that I was raising premium hands only in late position.
As a rule, though... just don't show. Make people pay for information.