I'm bored at work, so I figured I would illustrate my response above with some pics! Granted, these are some very extreme examples, but they're better to illustrate the point.
This first pic, you'll notice the keyboard is in focus, even though that's not where I wanted the focus of the picture to be. The text on the pen is blurry and difficult to read.
In this second picture, I tapped on the screen on the pen that I wanted in focus, and you'll notice the focus shifted from the keyboard to the pen, which made a much better picture.
Again, this is a very extreme example, and I had to actually cause the picture to do this, but it illustrates just how much exposure can be affected in a beneficial way, if you touch-select the subject of the photograph. In this first picture, the camera exposed for the light in the ceiling. You can see some detail in the light fixture, but everything else in the photo is way too dark.
Now for the second photograph, I tapped on the screen at the filing cabinets, and the camera automatically adjusted the exposure for the subject of the picture. It blew the light out, but since the light fixture was not the subject of my picture, the camera exposure did exactly what it was supposed to do.
This small tip of what to do will bring you photographs that are MUCH better balanced in color and in exposure, and will give you the sharpness you're looking for when photographing a certain subject.