Why do we need pattern? cant we just code?
Well we need it for ourselves. It just like constructing a new house and you go to some engineer for the blueprint. Nobody stops you from creating your house but most of us will take the advice of the people who has sufficient knowledge in this area.
Similarly a design pattern is a general reusable solution to a commonly occurring problem in software design. A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations. It is template, industry best practice, a tested solution.
when should i start thinking about patterns?
You should think about the patterns the moment you start thinking about the new project. Typically you should have a foundation of the application before you start coding.
Is it worth spending so much time for so called "designing patterns"?
I have found many projects worrying about performance, tight coupling, re-factoring code, difficulty in adding anew modules ... endless complaints when the project goes live or nearing completion. At this critical juncture companies spend millions for fine tuning the application. All this could have been avoided if a proper though on the architecture was given before the coding commenced. Don't think that only naive developers make mistake. I have seen experienced developers working in CMMI5 level companies making such mistakes. Many times even i was forced to do such things because of "pressure". This has to be thought by all the stake holders.
A properly designed application wont give us last minute surprises. so i strongly advice to create a strong design pattern before you start
Practically How can it help me?
Design patterns can speed up the development process by providing tested, proven development paradigms. Effective software design requires considering issues that may not become visible until later in the implementation. Reusing design patterns helps to prevent subtle issues that can cause major problems, and it also improves code readability for coders and architects who are familiar with the patterns.
Is it a silver-bullet for all my problems?
It wont solve all the problems which you may face, but it will surely provide you the tools and insight by which you can face & solve you problems. It is better to be prepared than feel sorry later.