when should you consider using a caching layer for your database?

hey folks, ive been thinking a lot about performance lately, especially how different caching strategies impact database load. weve all seen articles about Redis and Memcached, but im curious about the tipping point. at what scale or under what specific read/write patterns does introducing an explicit caching layer before hitting the DB become a necessity, rather than just a nice-to-have? what are your experiences?