Let's talk about this image for a moment:
This is floating around the internet and it gives a false impression.
Sight picture #1 is called the 6 o'clock hold. it is most commonly used by target shooters. It's fine for a gun with adjustable sights that will always be used to shoot at the same target. Bullseye shooters like this because it's easier to put the sight at the bottom of the circle than the center. However, it is not a good combat sight picture because targets are rarely the same size. So, as the size of the circle changes, so will your Point of Impact (POI).
Sight picture #2 is called the center hold. This is how 99% of the handguns on the market today are sighted. With the tops of the sights aligned and the top of the front sight on the center of the target. This is the perfect combat sight picture because the center of the target will always be the center no matter how far away or what the size is.
Sight picture #3 is relatively new to the pistol market and is most often called the combat sight picture. As I type this I only know of one manufacturer that makes combat pistols designed to use this sight picture. The idea here is to line up the dots and put the front sight dot on the target. The graphic above is highly misleading. Here's why:
Look at this picture:
This is an actual picture I took of an M&P. Notice that the dots are not lined up perfectly. Even though they are not, if they were lined up perfectly, the tops of the front and rear sights would not be lined up properly. So, there is a disparity between the dot method and lining up the tops of the sights.
Further, notice that the dots are not the same size like they are in the graphic at the top of this post. The reason for that is that they are actually the same physical size. Therefore, because the front sight is further away, it appears smaller. This is not a camera trick. Look at your own sights and you'll see this is true.
The conclusion to be drawn here is that the dots are not to be used as a sighting device. They are there to help acquire the sight picture quicker, that's all. In fact, misaligning the sights by attempting to line up the dots will actually throw your accuracy off further. It has to do with angles and distance. I'll go into that if this is not clear enough on its own.
If the dots and the top of the sights are both correlated, the actual difference between the two sight pictures would only be fractions of an inch at the target. As I've shown, they are rarely correlated.