A recent scholarly history of the LDS Church has noted:
For many years [in the nineteenth century] it had been common for members to rededicate themselves to building up the Kingdom through rebaptism. This practice was not considered essential to salvation but was a symbol of rededication. On other occasions the Saints were rebaptized as a symbolic gesture related to blessings for their health, entry into the United Order, preparation for marriage and even for going to the temple if they had not been there for some time.
As we study the records and journals we find this latter statement an accurate general description of rebaptism among the Latter-day Saints. Rebaptism was manifest during the lifetime of Joseph Smith, Jr. It was particularly prominent during the Nauvoo years and served many functions, including rebaptism for rededication, renewal, reformation, health, and preparation for temple ordinances.
