The main use case, and most probably the one that triggered the introduction of this feature, is upgrading to a new SQL Server version. An upgrade is never a trivial action; it brings improvements (that’s the reason why you upgrade, right?) but sometimes also regressions. These regressions are not always predictable and it happens often that companies do not perform a full upgrade to the latest SQL Server version, but instead leave the most important or most volatile databases in the old compatibility mode. This means execution plans will use the logic, rules, and algorithms from the previous database version. By taking this approach, you can reduce the risk of performance regression, but you will ...
SQL Server version upgrades and patching
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