It's quite simple:
Services need to be switched on (by you) for each client who gets that Service - e.g. accounts production
Automatic services are switched on for your clients automatically - e.g. new client take-on
Services most often represent the services that you sell in your practice.
On the other hand, Automatic Services do the day-to-day admin in your practice, such as taking on new customers or sending Christmas greetings.
Other than that difference, Services and Automatic Services are the same – they contain one or more Jobs... and those Jobs contain Tasks.
Choosing between services and automatic services
When you create a service, you can either choose for the service to start automatically for every client added, or only when you switch on the service on the client record:
If you don't want all clients to get an automatic service
Having automatic services running for every client may not be suitable, so you can decide which clients the automatic service should be applicable to. You can add filters to limit the matching clients.
For example, you might want onboarding to only happen for current clients, not prospects or former clients: