so like, when do you actually need a service mesh tho

Hey everyone, I've noticed more people talking about service meshes, like Istio and Linkerd, lately. We've got a Kubernetes cluster with a bunch of microservices, and it's okay for now, but I'm wondering when it gets too complicated. Like, when does the hassle of handling communication, monitoring, and security between services ourselves become more trouble than it's worth to just add a service mesh? What have you all found? When did you finally decide to pull the trigger, and what were the biggest upsides or downsides you ran into?