Following are the processes required for sandbox solutions:
Sandbox Worker process service is a Separate Service Application that actually executes Sandbox code. This service application should be started in every farm for using Sandbox solutions.
Sandbox Worker process proxy works as a proxy for Worker process. It takes care of Sandbox code execution and can also serve to other farms if configured. It helps the site administrator for load balancing.
Sandbox User Code Service takes care of user code in Sandbox. This service can be started in the farm s for using Sandbox solutions.