So, when should you think about using a service mesh?

Hey everyone, I've been thinking a lot about operational overhead lately. We're growing, and managing how our services talk to each other, especially keeping it secure and observable, is getting complicated. We're not quite at the microservice scale where I think a service mesh is a must-have yet, but I'm wondering when you all find it makes sense to bring one in. What are the main signs for your teams that it's time to look into something like Istio, Linkerd, or Consul Connect? Are there particular issues with observability, security, or traffic control that service meshes really fix well once you hit a certain size? I'm really curious to hear what you've experienced and what trade-offs you ran into.