Whether you are changing the configuration of your kitchen or planning to keep the same layout, a kitchen designer's expertise will make your kitchen more efficient by maximizing storage and functionality, while taking the beauty of the final product into consideration.  Designer's know what works and what doesn't!
Think of your project as a puzzle with so many intricate pieces which need to come together to create a beautiful living space for you and your family.  A kitchen designer has experience in placing all of these pieces.
Communication and comfort are crucial between a designer and the homeowner.  A good designer will listen to your likes and dislikes.  They will take into consideration any design theme or motif you are attracted to.  Finally, they will draw a full set of plans which include elevations or perspectives to help you visualize your new kitchen.
You may be asking yourself...."how do I choose a designer?"...."do I need an architect?"...."can my contractor help with the design phase?".  So many questions!  Let's start with the last question.  Most contractors prefer not to get involved in the design phase.  They will send you to a cabinet retailer to work with their "designer".  The showroom designer is a good source for ideas for your new kitchen.  Often these designers will not  recommend products they do not carry in-house, which may limit the final look of your space.  
What about an architect?  Architects have excellent technical abilities and are able to see the big picture, they often do not have the knowledge of what is available in cabinets, appliances, countertops, tiles, etc.
So where do you find a designer and how do you choose one?  The National Kitchen and Bath Association (NKBA) offers a list of certified kitchen designers who have completed various courses and have a certain amount of field experience.  The majority of homeowners, however, hire kitchen designers based on recommendations from friends and family.  But the most important factor in your selection process is to be comfortable with your designer.  The wealth of experience and information that a designer will bring to the table will give you a sense of security and will reduce your stress level during this time.  
Keep in mind that at the end of the day,  the designer goes home and you must live with your new kitchen everyday.  Therefore, your kitchen should be a reflection of yourself and the designers!!!