If the committee has already given you a score...lets say at a place like OHSU where the score is final, then whatever you send after they review your file is essentially worthless because that score is set in stone. The OHSU admissions people specifically told us this.
Although, there are many different versions of "hold." At some places "hold" means that the file will be reviewed again at a later date. At those schools extra material is definitely beneficial to your cause.
In conclusion...it depends on which school's "hold" you are referring to.