When is the OpenTelemetry Gateway actually required?

The setup instructions for OpenTelemetry (non-aws/k8s) include the deployment of one or more Gateways. If I'm only running a small number of servers (< 10), do I still need to deploy a gateway? Or can I send my traces directly to Sumo from the Agent on each node - a configuration which appeared to work on my dev machine?

Also, if I am deploying a gateway, what are the criteria for when I need to deploy more than one? It looks like a single Gateway instance can be configured with multiple pipelines, each relaying a single receiver to a single transmitter?