when should you add a caching layer, really?

hey everyone, ive been thinking about performance optimization lately. weve got a few services that are read-heavy and could benefit from faster data retrieval. im wondering about the tipping point where implementing a dedicated caching layer (like Redis or Memcached) becomes more beneficial than detrimental. what are your thoughts on when to introduce caching? are there specific metrics or scenarios you look for before making the jump?