Are there other similar topics that picture books cover?

“Picture books often are considered to be only for the very young. Yet picture books—from rugged board books for babies to the mysterious tales of Chris Van Allsburg and Shaun Tan, which adults appreciate wholeheartedly—exist for a wide range of readers”.
What are the advantages and disadvantages of using picture books in middle and high school?
One advantage might be that there is such a wide range of picture books now, some dealing with complex themes like gay marriage and homosexual parents. This might be a relatively safe way to introduce that topic in middle school. Are there other similar topics that picture books cover?