One of LinkedIn's hidden gems is the Answers feature. Simply put, you can both ask questions on a wide variety of topics and answer questions from people in and out of your network. A little bit of background before I get to the really good reason.
I first used Answers several years ago when I was having very strange problems with an early Windows phone (I think the last part of the sentence kind of explains it, don't you?). The Bluetooth setting in the Control Panel would turn off on its own, with no rhyme or reason. This was very aggravating when I got in the car, the phone would ring, and I'd realize that I couldn't use the Sync system in my car.
I posted a question in a couple of appropriate spots in Answers, and got incredibly detailed responses from people I didn't know. I was stunned. These answers ultimately helped me convince Verizon Wireless to replace my phone for free with a different model.
So here is the really good reason to answer questions. Someone posts a question. While there are users out there who abuse the system (people posting homework questions, asking questions clearly designed to promote themselves, etc.), there are people who are looking for help on a topic. Not only can you answer the question, it positions yourself in the eyes of both the person and others reading the question as an expert.
It gets better.
(At this point Joel apologizes for not being able to figure out how to copy something from the Answer page. If anyone can tell me how to copy part of the page on the following link and turn it into a .jpeg please comment or reach me through LinkedIn.)
Look at this question I answered earlier. Not only is my answer displayed, but so is my name (hyperlinked to my profile) AND my headline. I don't know that the person who asked this question is looking for someone specializing in audits of SEC Smaller Reporting Companies, but someone else reading the question might. Or someone reading another question I might answer. This is another reason to have an outstanding, distinctive headline that tells people who you are; see 9 out of 10 LinkedIn Headlines Are Dull - Is Yours? for more on that.
This is just gold. I'm going to make a point now of answering at least five questions every day in various categories.