What is the plan cache?

The plan cache stores compiled execution plans and related structures so SQL Server can reuse them for compatible statements.

Plan reuse reduces compilation CPU, but poor parameter-sensitive plans or large numbers of single-use ad-hoc plans can create problems.

DBAs and developers should investigate cache behavior using DMVs and Query Store rather than routinely clearing the plan cache, because clearing it can cause a burst of recompilation and temporarily degrade performance.