Continuing the theme of parallelization, statistics are now “sampled by a multi-threaded process” when using compatibility level 130.
Foreign Key Constraints One of the major selling points for relational databases is the ability to associate a table with other tables while using foreign key constraints to ensure data integrity.
By setting the database to a lower compatibility level, you lose the access to newer features.
This usually isn’t a problem during upgrades, as the database was designed with the older feature set in mind.
Joins and Foreign Key Constraints As mentioned before, foreign key constraints are not without a cost.