In my earlier post I mentioned reversed spine. The reasoning is for the slight increase in back cast power. And I do it because a good cast starts with a strong back cast. This is for pond 4 wts and otherwise 5 wt rods and above. For a stream rod I do a conventional spine because of the short casts and roll casts, plus it puts the weak side of the tip against the lighter and wiggling pressure of small stream fish. Big salmon and big trout or bass thump against the rod vs small fish wiggling.
If you spine the top two sections on some rods you will find a noticeable difference in the pressure it takes to bend the rod reversed spine than standard spine. You have to get a feel for it.
I believe my last switch rod I built was center axis and that turned out to the side, center axis as mentioned aligns the guides so there is no droop at the tip once built, often this results in reversed spine by default but it also could be to the side.
OK, so all that said ! I have built quite a lot of rods and used to build standard spine, taking time to get it "all" just right, to include the butt section and came to the conclusion that it will make for the smoothest casting feel in your hands. And imo, makes for accurate placement of dry flies with light 3-4 wt rods, very precise feel to the rod and the lighter side down for fighting little fish. I'm not a pro builder but over the years just came to realize this by testing rods with taped on guides and then moving the guides into different positions and recasting, move again and recast right out here in my back yard. But building the rods and going to the water I find I have come to like reversed spine. Still smooth but more powerful casts by a little but, especially lifting off the water. And it enhances my natural desire to want to push into my forward cast but doesn't damage the cast as much lol.