Difference usage of document level, sentence level and aspect level in sentiment analysis

Question

I'm studying about Sentiment analysis. What is the purpose of using Document Level, Sentence Level and Aspect Level?

I read this definition in Web Data Mining book by Bing liu.

In this book it was stated that,

Sentence Level sentiment analysis is to classify a sentence to negative, positive, neutral class.

Document level sentiment analysis to classify a document.

Aspect Level sentiment analysis is to classify each aspect of entity mentioned in a review.

Thanks.