Wireframes save a lot of time in the long run by fully defining the structure of the site before you move into the design and development phases of the project. Making changes early on is much easier. Also, by using an advanced wireframing tool that supports interaction, you can help better communicate what you are building to the client before actually building it.

The importance of Wireframes, is giving a clear idea the client of the structure of the website at the beginning of the project. It will help you and the client agree before going back and forth changing colours, fonts etc in photoshop. And also it will not let the client decide on such things before agreeing with him/her the structure and navigation of the website.

It's all about figuring out the structure, and finding the balance between the various page elements. Wireframes and mockups allow you to do this.