Experts stress that there are limitations in using impact factors to evaluate a scholar's work or a specific journal. This is one reason why other journal evaluation formulas have been devised. This allows authors and scholars to decide for themselves what metrics they want to use to evaluate a journals impact to their discipline. There are many reasons cited for not relying on an impact factor alone to evaluate a journal or an author's credibility.
A single factor is not sufficient for evaluating an author's work.
Journal values are meaningless unless compared within the same discipline. Impact factors vary among disciplines.
The impact factor was originally devised to show the impact of a specific journal, not a specific scholar. The quality and impact of the author's work may extend beyond the impact of a particular journal.
Altmetrics track things that traditional journal metrics do not, like how frequently your article was downloaded, whether or not your research has been covered in the news or other media outlets, scholarly discussions, social media shares, the countries that are viewing your research, whether or not your research has been bookmarked on scholarly websites or social websites like pinterest, and just a simple page view count. Many times, traditional journal metrics do not show the full picture of the impact of research and altmetrics can help to capture the elements of societal impact. In this way, altmetrics can complement traditional journal metrics.
Altmetrics capture elements of societal impact and can be captured more rapidly than traditional metrics. Examples of altmetrics are: