Here's the short answer:
An architect possesses a diverse set of skills which benefit the entire design and construction process. From studying site constraints to producing initial concept options, from reviewing material finishes to creating the final punchlist, an architect protects their client's interests, guides the process smoothly, and increases the value of the final product.
Here's the detailed answer:
An architect protects their client's interests.
Most projects begin with a list of client needs. An architect collaborates with the client to understand these needs, define project goals, and make design selections which satisfy those goals.
Throughout design and construction many detailed decisions will need to be made which will each have a tangible effect on the final building. An architect brings knowledge and experience which serve as resources to the client when making these decisions.
Additional services (structural engineering, environmental consulting, etc.) may be required on the project. An architect advises the client in the hiring of professionals best suited to that work.
A general contractor must be selected to provide cost calculations and construct the work. An architect can assist in this selection process and serves as an advocate to ensure that what the client has paid to be designed is what gets built.
The construction or renovation of a home involves a significant personal investment of both time and money. Having an architect involved gives the client peace of mind and allows enjoyment of the process from start to finish.
An architect guides the process.
Many questions will arise and their answers need to be timely and in-line with established goals for the project. The architect is the main point of contact for questions from the client, town officials, the general contractor, and other professionals working on the project.
As the design is developed, it is necessary to choose window and door manufacturers, siding, material finishes, hardware, and many other items. An architect guides the selection process and advises the client on where best to spend and where to save.
An architect increases the value of the final product.
An architect coordinates visual decisions (materials, building language, aesthetics), practical decisions (site constraints, green technologies, timeline), and economic decisions (project budget, durability and longevity of materials) into the design of a building.
To create a design which resolves all these factors an architect works equally toward the big picture and the small detail. An architect thinks simultaneously about the specific form and location of the building as well as the detailed functioning of each cabinet and light switch.
There is no single answer to any design problem. An architect typically produces multiple alternatives and recommends the best solution to meet the client's needs.
Here's the conclusion:
Far more than simply drafting plans or ensuring code compliance, the architect designs a building to have lasting value, compliment its site, and enhance the lives of its occupants.