I just rebuilt the first fly rod I built a while ago. I put a beadhead through the tip a month ago. This rod has been my go to lake rod as it is 10 foot and although a medium action can consistantly throw 70+ foot casts all day. (It's funny to watch my mates who are avid members of the Sage brigade cast it for the first time. They end up in a @#$%& of a mess as they wave it back and fourth as quickly as they can to try and get line speed before wrapping the line around themselves. Then you'll get an old guy from the cane school come down and shoot 80 foot of line with it.)
This rod shoots and has caught a lot of fish already but I have looked at this rod for a while and realised that I made mistakes with guide placement and the finish job and have been wanting to rectify it. When I was sent an entirely new blank I jumped at the opportunity. When I started to break it down I realised I had, for some reason that I can't remember, used an extra guide. My question is this:

Some guys believe in using extra guides to prevent line slap while others think extra guides create friction. What is your opinion?

Ben,
There is NO such thing as an extra guide. There is no such thing as too few guides.

There is only the number of guides that are on a rod.

If you try a rod and don't think you have enough guides, add a guide or more.

If you try a rod and think you have too many, take off a guide or more.

Be safe
REW

Bottom line - if you are going to err, use fewer guides than too many. You need one guide near the reel, one near the tip and one in the middle. Then, fill in with just the fewest number needed to complete the rod.

70 ft plus Sounds like you did something right
the best way would be to ty on guides with and without that extra guide and cast it See if it makes any difference in distance

Bill - willierods.com

Ben, There is a theory or at least a hypothesis that if you place a guide about four inches in front of the stripping guide, you will increase the casting distance. This "extra" guide is not accounted for when you use the static distribution test for setting the guides. The explanation for this is that this extra" guide prevents any line sagging of the line between the stripping guide and the next guide.

I have built many fly rods that way and I have also built many fly rods without the "extra" guide. On longer more powerful rods I am more likely to add the "extra" guide since I tend to make longer casts with such rods. I also usually use both Single and/or Double Haul casting techniques when I am using large powerful rods..

The problem I have with this idea is that a person's ability to cast a rod has far more effect on the casting distance than almost any other factor.

Mike Blomme

"Line slap" is more dependent upon line selection than guide placement. For proof try casting a tropic line on a steelhead river in December, or a cold water line from the deck of a flats boat in July. I suspect an accomplished caster could lay out a 70' cast with a rod equipped with one guide and a tip-top - and the right line.