Consider a case of a new researcher that does not know well all possible journals and has no access to human advice (from colleagues). (please do not comment that this is the best - out of scope of the question!)
Or one journal rejected the paper and the author is looking for outside the box candidates.
1. E.g., in medicine, one can use this tool (ETBLAST) by submitting full text of the article http://etest.vbi.vt.edu/etblast3/
Some journals even require top 3 similar papers (found by ETBLAST) to be pasted into a form during submission (making sure authors well addressed related literature).
2. Or Elsevier JournalFinder service.http://journalfinder.elsevier.com/