According to Google's website, the purpose of Google Scholar is to allow you to:

• Search all scholarly literature from one convenient place
• Explore related works, citations, authors, and publications
• Locate the complete document through your library or on the web
• Keep up with recent developments in any area of research
• Check who's citing your publications, create a public author profile

Strengths of Google Scholar

• Can help beginning researchers identify journal titles and authors connected with subjects of interest.
• Helpful for finding "grey literature" like conference proceedings. It includes many articles that wouldn't get included in other indexing services.
• Easier to find obscure references that are difficult to find in conventional databases.
• Can access books and articles in a single search.

Weaknesses of Google Scholar

• Can't sort/search by disciplinary field or browse by title
• Ability to limit search results is not as robust as in a library database
• Doesn't show you everything available to you through library resources
• Not everything you find will be accessible through the library or open access
• We don't know what Google is including in its searches or how it ranks those materials; we also don't know how often Google Scholar materials are updated