Re: loop to loop connection
Loops are easier and they enable you to switch out leaders quickly. I change up leaders a lot during a day depending on situations and dry vs nymph fishing. I have never noticed much of a difference casting and I used to cut the loop off and tie on leaders but what I noticed the most was the lack of flotation after cutting the loop off.
A couple of years ago at the Denver Fly Fishing show I stopped at the RIO booth and asked the question about cutting off the loop and flotation of the line. I was told the cutting of the line will introduce more water into the line and flotation will be compromised. This is the only issue with the nail knot technique that I know of.