Let me first start this post off by saying, I am no expert! I still have so much to learn, it's overwhelming sometimes. However, if something I am working on can shed light into someone else's photography then I am all for sharing :-) I've had a few questions about manual exposure, so here's my attempt to unravel the importance of it!
Before I even started my business, I followed the work of many incredibly talented photographers. I always saw them mention phrases like "manual exposure" or "i only shoot in manual mode". I never really understood why, but I thought if so many photographers are doing it then it must be important! When I bought my first camera I just stared at the "M" on the dial for the first month or so. It's a little intimidating. But one day I mustered up the courage to turn my dial ALL THE WAY from "P" to "M" and I haven't turned back since. Mastering manual mode is one of the BEST ways to learn how your camera works. It's one of the fastest ways to understand how aperture, shutter speed and ISO all relate to one another. And it allows you complete control over your images. For those of you that know me, you'll all agree I like to be in control ;-) By manually exposing all of your shots, you are able to better capture what your eye sees in your subject - not what your camera sees. How many times have you snapped a photo in full auto mode and looked down at the back of the camera to see a photo that looks too dark? Or looks different than how you anticipated? Manual mode to the rescue!!
In order to illustrate my point, I snapped a couple pictures of my lovely husband. He's sitting across from me at our desk with the window behind him. Since it was later in the afternoon, the sun was coming in pretty strongly from behind him. Below are two photos side-by-side straight out of the camera. The one on the left was taken using full auto. The one on the right was taken using manual mode.

In the picture on the left, the camera sensed a LOT of light coming in and compensated for it. Essentially it automatically exposed for the window making Robert, the subject of the picture, too dark. In the picture on the right, I controlled the settings and exposed for Robert, not the window. Now, obviously the light coming in through the window makes that part of the image really blown out (over-exposed). But, since the window isn't my focus, I don't really mind! :-) I happen to like the version on the right muuuuuch better than the version on the left!
So, for all of you that own a camera with manual capabilities I highly encourage you to explore manual mode! It can be frustrating at first but it's oh so rewarding once you get the hang of it. I shoot exclusively in manual and love the freedom it gives me to manipulate my shots in camera.