Why is premature materialization considered a LINQ anti-pattern?

Premature materialization loads data too early, preventing query optimization and increasing memory usage.

Calling ToList(), ToArray(), or ToDictionary too early ends deferred execution. This forces the entire dataset to be loaded before filtering, projection, or aggregation occurs. In database-backed LINQ, this results in inefficient SQL usage or even full table scans transferred over the network. It also disables server-side optimizations like index usage and query planning.