Specifying indexes has these risks:
Changes in the distribution of data could make the forced index less efficient than other choices.
Dropping the index means that all queries and procedures that specify the index print an informational message indicating that the index does not exist. The query is optimized using the best alternative access method.
Maintenance increases, since all queries using this option need to be checked periodically. Also, future versions of Adaptive Server may eliminate the problems that lead you to incorporate index forcing, so you should check all queries using forced indexes each time you install a new version.