Appendix carry of a firearm (hopefully a pistol) is the act of carrying the gun somewhere usually within the vicinity of 11-1 o’clock on the body. Generally speaking this is from a concealed inside the waistband position. The carry method has become increasingly popular over the last decade as the average shooter has come to realize firearms do not usually discharge randomly and the threat to their nether regions is far less than previously believed. It also has some very practical applications and is an excellent carry method for effective concealment and extraction of a firearm. It also has some drawbacks but all of it is very conditional to the individual situation and the needs of the shooter.
As a concealed carry method, appendix carry is probably one of the most versatile as well as concealable methods of carrying a firearm on a daily basis. It seldom prints (forms an outline in clothing when covered) or becomes exposed and caters to lighter clothing which is extremely beneficial in warmer conditions where a second clothing layer, such as a jacket or sweatshirt, is not as applicable. Its location gives the shooter an easy process to locate and draw the firearm. With practice the shooter can become subconsciously fast and turn the draw into a smooth process. This is all a bit dependent on the firearm and its geometry combined with the clothing, but generally holds true. I should note that it makes the firearm, essentially, is just as accessible from a seated position as it is from a standing based one.
The short comings of appendix carry are dependent on the shooters clothing and situational needs as well. It does not cater well to suits given that the shirt is tucked in and the jacket must be cleared to draw; also a suit jacket left open in this manner risks exposure of the guns existence. It does not work well for duty use because the need to access a sidearm quickly leads to a more open style of carry, gear often gets in the way of the shooters center line and can restrict access to waistline based equipment, especially a concealed firearm. Outside the waist band and hip carry methods often lend themselves to faster and cleaner draws when it comes to this application, especially in conjunction to a primary weapon such as a rifle. Again, this is all situationally dependent and should be interpreted as such.
Overall appendix carry is a well-rounded method of concealed carry and with the use of modern equipment/holsters it is extremely efficient. Really it depends on the individual and their needs. Regardless of the method employed, it is up to the individual to get out and train in their chosen method to the point of subconscious proficiency.