I am wondering the reason why most of the jounals ask for 4-5 potential reviewers' details during submission of a manuscript? Whether does the editor really send the manuscript to the suggested reviewers? I always select potential reviewers from my reference list whose work/methods is largely similar to my work. But still the reviewers ask some unexpected questions in their comments.
The editor, who selects the reviewers, may not be familiar with the particular sub-area, when a journal is not hyper-narrowly focused. In that case, providing a list of potential reviewers directs the editor's attention to possible scholars in the area. Once your attention has been drawn to an individual, you can spend some time discovering whether they would actually be good in that area.