When does a monorepo make sense, considering it adds more build steps?

We've been talking a lot about using a monorepo for our new services. I mean, putting all the code together makes handling dependencies way simpler, and it's easier to make changes across everything. But honestly, I'm worried about how long builds will take as the code grows. And that initial cost for tools like Bazel or Nx? It seems pretty steep. So, when do you think a monorepo is actually worth it, especially when you weigh the complicated build stuff against the good things for development?