Researchers experiment with individual and group of designers. In 'engineering design' what are pros and cons (in general) for doing experiment with two designers in a group? By engineering design, I mean a design problem based on mechanical, industrial design etc. By solution, I mean concept generation.
A lot of it depends on interpersonal relationships, whether there is antagonistic competition, or some form of cooperation. If we can assume they are striving in good faith toward the best answer, then (as is usually said) two heads are better than one. It is almost impossible for one person to catch all the issues: everyone has their areas of best focus...and their blind spots.
Modern engineering design education today relying primarily on the project-based coursed, performed by the group of students. For a reason. It is almost impossible to imagine a relevant industrial task implemented by one (even skilled) individual. It's simply not a real-life scenario.
That would depend heavily on your area of study. If the objective is to create solutions or for generalised studies, then more people are better(under optimum group dynamics). Problem-solving as a group brings in diverse perspectives and is also great at catching individual biases.
But if your objective is to observe design processes from a human perspective, studying individuals can throw up some interesting observations.
Designing a product needs expertise in every , I mean every branch of the business that means, Production, Quality, Purchase, Packaging, Marketing departments. A designer or a design team will consider all the above departments capabilities, their constraints while designing a product. Even though If a designer is a hero (as we see in the movies) who does all the work in single hand. In practical , If a company has one designer, the designs will take days and some time months to reach shop floor with some errors, not full designs. So, their should be 2 or more people in design team, One can look after the 3D design, another can look after the drafting part. For your understanding, I would suggest you to read, "Product Design for Manufacture and Assembly by Boothroyd " book. It has a great insight in designing a product. Kindly see that the above is in Imperial(inch, foot, lbs) format.
it is depend on the capability of the designers and the difficulty of designing project . generaly one good desiner can quickly finish the simple design, the group designers can do good design of complex project, but there must be one supervisor to lead and monitor the designing process, quality and cost.