Twitter is a tricky little concept to grasp for some folks. Usually until they start using it and find a use for it. The idea that people tweet about what they had for breakfast or other mundane little life events is not really a misconception. It's a small part of a larger truth. In order to get that little piece of information (eggs, toast) you have to subscribe to a person's feed. If you know the person, the information is still useless, but at least you know who said it. If you don't know the person, then why would you follow them? If you get random useless information on twitter it's because you asked for it. You get what you ask for. Following is nothing more than asking to be in someone's loop. If you don't like what they tweet about don't follow. If you don't want people following you, block them or make your information private (invite only).
I'll ask the question again, why would you follow someone you don't know? There are several reasons to do this.
1. If someone posts relevant information about your industry, you'll be in the know. Relevant information will come to you.
2. If you want to expand your network. Follow people whom you would like to network with. People tend to group themselves by mutual interest, twitter is no difference. It's a great way to get you name out and to meet people in your field. Following the right person could land you "the" job. But, it's not all about networking online. Many professional groups have regular offline meet-ups at bars or other places of interest.
You are basically creating and managing your own personal/professional network 140 characters at a time. You filter what comes through, you decide what goes out if anything and everyone else does the whatever they want. Some people don't follow anyone, some follow everyone. Tune in and out as you please. It's as complex as you make it.