There are a million reasons to get a dog and a million reasons not to. :) I personally want the companionship, love and affection, and I want to give that back to the dogs too. I also love developing a deep bond, relationship and strong communication with another species. I live in the city, so livestock-type pets are out of the question. I do like cats, but prefer the types of activities I can do with my dogs.
And did I say I love to develop a deep communication with dogs. :) I find training (ie communicating - and it is a two way street) with dogs is fascinating.
Reasons NOT to get a dog? To breed. To put in the back yard. For protection only. Because a puppy is cute... etc.
Remember, a dog is a 15 year commitment. It will take years of time and work and continued training to have the dog fit into your life. It can and will do bad things and may develop rather bad behavior issues that will need to be fixed. It will also cost money - and possibly a ton of it if a health issue arises.
However, all the questions you are asking are proving you're going about this the right way. :) Getting information, reading and knowing about dog ownership before getting the dog is fantastic. Kudos to you!!!