The “Free” design is typically offered by an equipment distribution house and the cost of the design service will be included in the mark-up added onto the equipment costs, typically called Design & Supply.
The “Paid” design service is what you would go to a Consultant for, where you would pay a fee for a design and associated documents (depending on the level of service required)
Our scenario is probably directly comparable to Architect – Builder comparison! So if you find your project needing an Architect you will probably find that the “Paid” Consultant route is best suited to offer a complete design solution. If on the other hand you are only doing some small modifications to your kitchen and have a builder in you would probably find the “Free” design and build services from an equipment distributer more suited to your needs.