Some of the posts are based on four fletch having more total feather area. If they both have the same total feather area, four fletch and three fletch have the same drag. Four fletch has slightly, probably insignificantly, better stabilization due to more of the feather area being further back on the shaft, and 4 fletch has 18% less cross wind susceptibility That is because of the way the feathers partially block each other from the side. That’s from a simple calculation in which the arrow is rotated through 360 deg. However, when I have tested it in moderate crosswinds, I can’t really tell the difference.
More economical due to getting more short fletches from a full length feather.
An extra glue joint to worry about.
Takes longer to fletch a set of arrows.
Can’t use an AZ EZ-Fletch jig (I don’t want to, but some like them)
Poorer feather clearance, although again, I can’t tell the difference in field testing.
You can use nocks without an indicator and not care.