Seems like everywhere you look nowadays you see people carrying their pistols in the 12 o'clock position, which is crazy for the traditional 3-5 o'clock. Why? Is it just the cool thing to do? So I had to try this out for myself.
What I did was bought a Glock 43 and a holster from Bravo Concealment for this experiment. Now I'm not the type who wears 5.11's and tactical belts everyday. I'm more of a jeans and T-shirt, so I didn't change anything when it comes to my daily wear.
The first time wearing this setup I placed the pistol at about 1 o'clock and went about my day. The first thing I noticed was every time I sat down the holster dug into my right thigh. Kind of annoying, but I kept it going for the rest of the day. By the end of the day I regretted that decision. This was not going to work for me.
The next day I put the gun at 12 o'clock, with the belt clips on either side of my belt loop. Immediately I noticed a difference in comfort and the digging into my leg was no longer there. It took another day or so to get used to the pistol sitting off my stomach, but after that it became very manageable. I've been wearing it as a EDC for about 3 weeks now, with no issues.
So why do this? Because of the draw. Your hands naturally rest in front of you, so hand to pistol time is extremely fast. It also allows you to "present" the weapon correctly by drawing up then out into your target. Carrying your pistol in the traditional 3-5 o'clock is comfortable but when it comes to the draw, puts you at a disadvantage. A couple things being, bringing your hand/arm behind your body and extra time to present the weapon on target.
In short. Why is everyone starting to carry appendix style? Because it works.
Pros: Concealability, quick draw, quick presentation.
Cons: Depending on body types, this may not work for you.