The big draw for many investors with AGNC is its huge yield, but how much is a huge yield worth to you?AGNC Investment (AGNC) is a very complex business, but its 15% dividend yield is like a siren's song to dividend investors traveling along Wall Street. There are a lot of good reasons why income-focused investors should avoid AGNC, and the mortgage real estate investment trust (REIT) added a new one when it reported third-quarter earnings. Here's what you need to know before buying AGNC.AGNC Investment is ...