It really depends on what you are trying to achieve, to my mind.
A pattern isn't a template, and it isn't a solution in itself. It is a way of approaching a certain type of issue in a cleaner or easier way than many of the "solutions" one comes up with right off the bat.
I think that a good grasp of the types of problems that you run into along with a good overview of the various patterns that successfully address those problems will allow you the flexibility to apply a pattern or not when it is needed.
Having patterns at your fingertips will allow you to recognize that you are about to get yourself into a mess, or it might help you once you realize what sort of mess you are in, to re-approach your design in a new way.
The design patterns in my book, CSS and HTML Design Patterns, are important because they dramatically increase your productivity. It doesn't matter how complex or simple your application is. Patterns make your job easier.
They are building blocks that can be combined to create any design you can imagine. They are similar to templates and recipes, but they go deeper � they are the patterns behind templates and recipes.
In my book, I bring each pattern to life by showing you many examples of how to implement the pattern using CSS and XHTML. These patterns and examples show you the most effective way to design web pages that are accessible, flexible, semantic, and reliable.
The examples I give for each pattern remove all the guesswork and trial-and-error out of building web pages. They make it easy for you to imagine what you want and then build it using proven patterns that work in every major browser.
Using these design patterns, you will be able to create web pages many times faster than can without them.
subject: How important it is to apply a design pattern?