when is it time for a distributed cache

hey folks, ive been thinking a lot about performance lately, especially around how to reduce database load. we're seeing increased traffic and im starting to wonder about introducing a distributed cache like Redis or Memcached. what are the key indicators that tell you its time to move beyond in-memory caching or just hitting the db directly? when did you guys pull the trigger on adding one, and what were the main benefits you saw? any pitfalls to watch out for?