Pros
If you''re already an ESL teacher, this offers a great change of pace from the heavily structured classes you are likely teaching in person. Freedom to just shoot the breeze and help someone improve their English while in the midst of a cultural exchange... it can be quite fun. Getting monetary compensation on Cambly is a great bonus to what I already do anyway- chat with people and make new friends while living/traveling in different countries.
Cons
Don't do this if you came to make money online and don't care about teaching or world culture, you are wasting student time and money. The pay is a nice supplement to a full time job, or is great if you live in a country with a low cost of living... otherwise, don't come here expecting a fat paycheck. There are sometimes connectivity issues, even when both student and teacher have high speed internet... I believe the problem to be server related.