Disadvantage: trolls, 101% of the people that reply are not experts.
Advantages: most of the times you are answered, privacy or anonymity in delicate subjects.
If its for college, credit your sources. Just kidding. But you can apply the same concept with how academia hates when people use Wikipedia as a source because it may be unreliable. You can say similar things about random people on the internet.
An advantage is that you have a discussion or communicate with people who share your interest. Another advantage is that you can reach a large number of people and hear a wide variety of opinions on a topic, but a disadvantage is that people can be rude because they are hiding behind a keyboard and they may say things to others that they wouldn't say in person.