You can develop the WCF service only if it solves multiple purposes or in case it's being called by multiple clients. It also help in reducing the load on a web server running your website if the business/data access logic is developed in a WCF service and hosted on a different web server. WCF service can be accessed by the different calling applications such as Java. .Net etc as it can be accessed by means of SOAP messages.
WCF is a generic communication mechanism that allows you to setup generic client/host communication between two parties. The neat thing about WCF is that is allows you to configure service properties such as transport (http/pipes/tcp/Tibco EMS), security models (any of the W3C standards), compression, encoding, timeouts, etc, without changing ANY code. That is powerful. Best of all, you can configure it so that you can have a service in C# and a client in Java (or any other language or the other way around), as long as they both talk using the same mechanisms.You can create a standard HTTP SOAP web service using WCF and one day decide to switch it to use the faster named pipes for local communication. You can create web services that talk over TibcoEMS and have easy failover on the queue level. You can create a file streaming web service that distributes all kinds of images/videos to your application.