What Preparing Saves
Running a query involves parsing the SQL, planning it, then executing. A prepared statement parses and often plans once, then accepts parameters on each execution. For a query run thousands of times a second, skipping repeated parse and plan work cuts CPU and latency.
Plan Caching Tradeoff
A reused plan is built from generic parameter assumptions. Usually that is fine, but for data with skewed distributions a generic plan can be worse than one tuned to the actual value. Some databases watch for this and switch between a generic and a custom plan based on observed cost.
The Pooling Pitfall
Prepared statements live on a server side session. If a connection pooler operates in a mode that swaps the underlying connection between transactions, a statement prepared on one backend may not exist on the next. Match your pooling mode to your use of prepared statements, or the reuse silently breaks.
Key idea
Prepared statements parse and plan once then execute many times, saving CPU on hot queries, but watch skewed data plans and pooling modes that break reuse.