When considering which kind of design expertise you need it can be helpful to think about the nature of the problem you are seeking to address. Some problems are more complex than others. Some are abstract, while others are more concrete. Depending on the nature of the problem and desired deliverable, there will be a range of design skillset combinations that might be suitable.
In the below framework, you will see where different types of design expertise might fall in relation to the level of complexity of the problem. Few problems fall solely into one design discipline’s skillset. The lines between them can be blurry, and as a result, designers are often comfortable in more than one design specialty. While there are many foundational skills that all designers share - such as thinking visually, or making ideas tangible - designers also have differentiated areas of specialized expertise - graphic design, service design, product design, etc.