whens sharding your database really worth the pain?

we've hit a point where our main database is starting to feel the strain under load. we're thinking about sharding, but the operational overhead and complexity just seem like a lot. has anyone here actually done database sharding? what exact metrics or pain points made you decide it was worth the effort. i'm curious about the before and after, and what challenges you faced during the migration and ongoing management. looking for real-world experiences to help us decide if we should go down this path.