Arguably the most common way to fletch an arrow, 3-fletch provides stability while not adding extra surface area to the back of your arrow. Less surface area may be a big factor to some, as less surface area results in a faster arrow.
However, if a decrease in arrow speed does not bother you, then you will be able to fletch higher-profile vanes to better steer your arrow if necessary. An example of needing a higher-profile vane would be if you are shooting a large broadhead on the front of your arrow. The bigger the blades are on your head, the higher the profile of your vanes need to be.Â
If the broadhead you are shooting is low-profile, and your vanes on the back of your arrow are too tall, you could see your arrow have a “parachute” effect downrange. This happens when your vanes over-steer the back of your arrow, and it appears like your vanes are “parachuting” behind your broadhead.
Overall with the 3-fletch method, you have the ability to fletch your arrows with a variety of different vane profiles depending on your overall arrow setup. Also, one could argue that you save not only time, but money when it comes time to fletch with only 3 vanes per arrow.