Before entering certain fields, a post-doc appointment may be a necessary step in order to gain greater knowledge and experience, make connections, and build a name for oneself in research circles. It may also be seen as a valuable tool to distinguish oneself from other candidates when entering the job market. Such appointments are often the "stepping stone" whereby a graduate student can improve his or her publication record and hence progress to a permanent academic post.
Completion of a post-doc position does not involve the granting of an academic degree, since the doctorate by definition is the highest degree awarded in a given field.