API might cost a lot of money for the amount of requests you want to send. API may not include some fields in the data you want. API is rate limited, scraping might not be. API requires agreement to usage terms, scraping does not (though the recent LinkedIn scraping case might weaken that argument.)
My understanding is that the result of the LinkedIn case is that you can scrape data that you have permission to view but not to access data that you were not intended to. The end result that ClickWrap agreements are unenforceable.
API might cost a lot of money for the amount of requests you want to send. API may not include some fields in the data you want. API is rate limited, scraping might not be. API requires agreement to usage terms, scraping does not (though the recent LinkedIn scraping case might weaken that argument.)
My understanding is that the result of the LinkedIn case is that you can scrape data that you have permission to view but not to access data that you were not intended to. The end result that ClickWrap agreements are unenforceable.