At the risk of getting us back on topic... Mark, why do YOU take pictures? And why did you ask?
I take pictures for the WDW Weekly Photo Contest, of course!
Seriously, I started taking pictures back in the mid '80s. I got started because it seemed like an interesting hobby and, like others have said here, and approachable art form for someone with limited artistic skills. I quickly found that it made me think a lot more about a lot of things - composition, light, color, how our eyes work, how our minds translate sight into vision, etc.
It found that it was also a great tool for telling stories. I love the challenge of capturing not just the appearance of something, but it sense or essence. While you are constrained by what you can see, you still have tremendous opportunities to record it in different ways. You can chose different focal lengths and shooting locations to control the field of view and perspective. You can choose different framings to imply all sorts of things. You can adjust your shutter speed to stop the world or capture it's movement.
I see much more now that I take pictures. I notice the cold, shadowless light before dawn. I see the warm colors of sunrise and sunset. I enjoy the shadowy textures of early morning and late afternoon light. Cloudy days go from dreary to a source of soft light and saturated colors.
Taking pictures has taught me a lot about composition. We all have an innate ability to "read" compositions, but learning to take pictures has taught me how to "speak" it's language.
Taking pictures is something that I do to help me learn to see my world and tell stories about it.
In addition to taking pictures, I shoot video. I find that the two are much more different than they seem. In fact, I have a lot of trouble doing both at the same event. With a picture, I'm trying to reduce my entire story or at least one "scene" from my story down to a single picture. With video, I'm letting a story unfold over time. To me, they require a much different way of thinking about the story.
I find that I enjoy the pictures from trips more than I enjoy the video. The one area that I love video is for bringing back memories of how life used to be. To that end, I'm working on several home video projects. These include:
1) Annual interviews of the kids - Who are your friends? What's school like? What are you going to be when you grow up? What's your family going to be like? That sort of thing
2) A day-in-the-life - A little movie following each of us through a "typical" day showing our morning routine, how we get around, what school is like, what work is like, what we do for fun, what chores we do, etc.
3) A tour of our community and our home with a focus on the what seems "modern" today.
I'm doing these because these are the movies that I wish I had from when I was a kid or when my parents were kids. I love the notion that my great grandkids can see my world with me as a tour guide. I guess it's sort of like a presonallized Carousel of Progress show.
So why did I ask the question? For two reasons. First, I was curious as to why other people took pictures. Not just the snapshooters, but hobbyist photographers. I was also hoping to get people to reflect on why they take pictures. I think that stepping back and asking yourself why you do something helps you do that thing better. Maybe not better in some absolute sense, but in a way that is better for achieving what it is you are trying to achieve.
How's that for a long rambling answer to a short question?