underexposing or overexposing without any intelligent thought behind it is something that should be avoided. Always approach it from a intelligent standpoint. We master the tools so that we can bring our artistic vision into creation. As someone said, the dynamic range on a digital camera is not as vast as it is on a film based camera, but that is ok. You do gain a stop with a full frame sensor as opposed to a crop sensor, however it still doesnt compare to a film camera.
Anyway, so what do I mean by the above. Well lets say you have someone on a bright sunny day and they have a white hat on and a dark navy blue coat on. Naturally, you will not be able to pull both into range, so one is either over exposed or under exposed. Well this is when we must learn to speak artistically. By this I mean, a photograph is a conversation without words. You have a subject and your attempting to convey something about that subject. So, in this case are you trying to convey something about the hat, jacket or the person wearing them? Which one is more important to you, maintaining detail in the jacket and the person or the hat and the person or can you do it in those combinations? Once you sort that out, then you expose for the subject and allow whatever in the scene that is not important to be over or under exposed. This is the science behind the zone system created by Ansel Adams and Fred Archer. It is very critical to understand how this works.
I should add this also depends on if the shooter is using natural light or studio lighting. Once you have artificial (off camera lighting) in the mix the dynamics change and you have more options. With off camera/studio lighting you now have control of the entire scene. However, understanding the zone system is important still when looking at the histogram, understanding what colors fall where on the histogram. This will tell you if your scene is over or under exposed or what colors are falling where. Also when post processing and adjusting brightness etc. Generally though, you are going to use a light meter in a studio situation. Well I should say most would. I see some people on the internet say they dont need one blah blah blah but generally speaking those are hobbyist not getting paid to do assignments. Nothing wrong with being a hobbyist but for serious work a light meter can make a huge difference. Some argue the light meter doesn't allow you to be artistic. I think that is total nonsense, I tis just like the camera, a tool used that allows us to create our vision. All that light meter does is tells us how much light is falling where. You can still dial in your exposure to over or under expose that area or to even boost the output from your lights for certain affects etc. (lets say your doing low key lighting for example). Anyway, if anyone is interested in learning the zone system, scroll up, I posted a amazing video on the subject. It will help you understand how your camera works and how the light meter in your camera works. Also will give you a TINY introduction into color theory.