Scholarly metrics are a way for the impact of an article, author, or journal to be measured quantitatively. There are different methods used in order to calculate a scholarly impact with the intent that these works will be judged solely on impact to the field as opposed to using criteria without universal standards.
There has been much debate about the use of impact factors in academia. Some academics feel that scholarly metrics place too much emphasis on the quantity of work as opposed to the quality of the work being produced. There is also a concern that focusing on metrics will pressure authors to publish "hot-topic" articles in only the most "impactful" journals as opposed to producing and experimenting with more original work.
Journal metrics and rankings are not synonymous with journal quality. To get a fuller picture of a journal's quality, researchers should examine the journal itself and think critically about its policy, leadership, articles, etc. The site Think. Check. Submit. lists questions that researchers should ask themselves when evaluating a journal, especially when considering whether to publish with that journal.