To answer this question, first of all we need to understand who is asking and what the term means. There are so many different ways in which people understand the term "Enterprise Architect". Most of the confusion is caused by vendors who brand their products with the prefix "Enterprise" as in ERP, Enterprise Management etc., I personally would like to call the Specialists who have High level design, configuration and developmental capability in foundational Technology products as "Technical Architects" or "Application Architects" as the case may be. ERP, CRM etc needs a special treatment because they cover both the Application Functionality and Application Platform in a single package. I tend to call the specialists in these areas as "Enterprise Solution Architects". In my view, an "Enterprise Architect" is an IT Generalist who can provide a conceptual view of the Business, Information and Technology landscape which is Product, Technology and Vendor agnostic. The enterprise here could cover the whole of the organisation or even a Division of the organisation.
Lets look at three main stake holder groups out of the possible many.
If the question comes from the CIO or their Leadership team of a User organisation, the answer is to use this person to define Enterprise wide Platforms of capabilities and to facilitate IT Strategy and Plans and their implementation.
If the question comes from the CEO or their Leadership team of a User organisation, the answer is to use this person as glue between Business and IT by making this person to understand Business Goals, Objectives, Strategies and Operating models.
If the question comes from Vendors, the answer is to position this person as a trusted advisor in client business to assist the clients in the above activities which will lead to downstream business.
Whatever the case may be it is clear that when "Enterprise Architects" like City Planners are used to provide concepts and capability definitions rather than Design and Solutions the benefits to the Enterprise are significant. Open Group's TOGAF provides all the necessary methods and techniques to realise this.