Not every team has a dedicated database administrator. I’ve **never** worked on a team that has had someone solely focused on making sure our tables are structured perfectly with all the forms of normalization being applied.
One of the concepts that are key to good database design is making sure our data is normalized.
Relational databases allow us to define foreign key constraints that prevent us from creating orphaned records.
There is a performance penalty to using foreign key constraints as the database is going to make sure we have valid data in each of the foreign keyed columns.