Wireframing is a very important step in the process of creating a website. Clients and designers often have an urge to jump straight into design because it's the cool creative bit where you get to see what your site is going to look like.
To skip the wireframe stage though is to set yourself up for problems further down the line.
Wireframes are essentially like blue-prints of your website. Using architecture as an analogy. Wireframes are like CAD drawings of a building while design is like a 3D rendering of the building. You need good CAD drawings in order to create an accurate 3D rendering and ultimately build the building. It's the same with wireframes (especially when it comes to large complex sites), you need detailed and well thought out wireframes in order to design and build a successful website.
Wireframing covers two main aspects, information architecture and interaction design (UX design). Information architecture is about organising all your content and categorising it so that it all links together nicely and makes sense and UX design is about how users will navigate through your website, how you will facilitate them to find what they are looking for and guide them to do what you want them to do.
The creation of in-depth wireframes that deal with information architecture and UX design essentially results in a prototype of your website. This prototype acts as a central hub for everyone involved in the project, offering something tangible to explore and consider and to show to others without getting distracted or bogged down in more aesthetic design decisions.
Once you have a wireframe prototype of your website, you can use it to do some preliminary user testing. This can help highlight and iron out any usability and website structure issues at an early stage of the project lifecycle (before you get to the point where making any changes may result in painful extensions to the project timeline and perhaps cost).
To conclude, resist the temptation to skip this step or whiz through it quickly. Take time to plan your site well, the more time you put in at this stage, the more time you save yourself later.