Both Memcached and Redis are popular in-memory caching systems, but they have different strengths and use cases. Here are some reasons why one might choose Memcached over Redis:

1. Simplicity and Performance: Memcached is designed to be simple and lightweight, focusing on high-performance caching. It has a smaller codebase and simpler architecture compared to Redis, which allows it to achieve lower latencies and handle high request rates efficiently. If you need a caching solution that excels in raw speed and simplicity, Memcached can be a good choice.

2. Distributed Caching: Memcached is built with distributed caching in mind. It has native support for sharding and data partitioning across multiple servers or nodes. This makes it easy to scale your caching infrastructure horizontally by adding more Memcached instances. If your application requires a distributed caching solution with seamless scaling, Memcached provides built-in support for it.

3. Protocol Support: Memcached has a simple and straightforward protocol, which is well-documented and supported by a wide range of programming languages and frameworks. It makes integration with different systems and languages relatively easy. If you have a multi-language or multi-platform environment and need a caching solution that has broad protocol support, Memcached is a good fit.

4. Cache Expiration: Memcached offers a straightforward expiration model for cache items. You can set a time-to-live (TTL) value for each cache item, after which it will be automatically evicted from the cache. If your caching needs primarily involve simple TTL-based expiration without the need for more advanced eviction policies or persistence options, Memcached provides a lightweight and efficient solution.

That being said, Redis also offers several advantages over Memcached:

1. Data Persistence: Redis provides additional features like data persistence to disk, allowing you to use it as a more versatile data store beyond caching. Redis can be used for more complex data structures, data manipulation, and advanced querying capabilities.

2. Advanced Data Structures: Redis supports a rich set of data structures such as lists, sets, sorted sets, hashes, and more. This allows for more sophisticated caching scenarios where you need to perform complex operations on cached data.

3. Pub/Sub and Message Queues: Redis includes built-in support for publish/subscribe messaging patterns and can be used as a message broker or a lightweight message queue. If your application requires messaging or queueing capabilities in addition to caching, Redis provides a convenient solution.

4. Advanced Caching Features: Redis offers features like automatic cache eviction policies, key expiration notifications, transactions, and Lua scripting. These features allow for more fine-grained control over caching behavior and enable complex caching strategies.

In summary, Memcached is a lightweight, high-performance, and distributed caching system that excels at simple caching scenarios with high request rates. It’s suitable for straightforward caching needs and environments where simplicity and raw speed are crucial. On the other hand, Redis provides a broader set of features, including data persistence, advanced data structures, messaging capabilities, and more sophisticated caching options. It’s a versatile choice when you require caching as well as additional data manipulation and messaging functionalities.