To over-line or not to over-line. Yes, that has been the subject of many a campfire or bank-side setting between or amongst fly anglers.
I know master casting instructors and most have told me to always line the rod with the appropriate weight line. Then, I have friends that have been fly fishing for many years and they say over-lining a rod helps their performance.
Of course, a lot of the success depends on the rod too. I've found with a "hard" or rather stiff rod, over-lining seems to help.
In an article written by Lani Waller, he shares what matters most is you - that guy or gal that will be doing the casting. "Forget science, if you can. And sometimes you can even forget the line recommendation on the rod – if you want to. What matters most in matching a rod and line are you, your style of fishing and casting and the kinds of conditions and circumstances you will encounter. Remember, the person who designed the rod, or the one who sold it to you won’t be there with you."
Read more from Lani Waller and his article: The Perfect Match