InnoDB Foreign key updating vs. manual in-application updating
It is better to let InnoDB enforce foreign keys. Trying to implement referential integrity in an application can be brittle and would obligate you to write


rollback operations
check constraints on keys
manual cascading of DELETEs and perhaps UPDATEs


InnoDB is equipped for all that and more. Plus, operations done in application logic is difficult to rollback, especially if one uses stored procedures or user-defined triggers.