Ranked in these QuestionsQuestion Ranking
Pro Good sharing and community support
Pro Moderately high cloud space
Pro Very good PDF management capability
Pro Great web interface
Pro Good video tutorials
Official video tutorials can be found here that take you through what the software is capable and how to go about using it.
Con Closed Source (Proprietary)
Own by Elsevier
Con Not very good web import capability
To support importing citation from your browser
Con Proprietary and not-standard PDF annotation
If you annotate the PDFs you have to open it with Mendeley since it uses non-standard formats to annotate PDFs.