The answers to these questions will be very different depending on the scenario. In general I would say that the ability to make full scale experience prototypes is invaluable in furniture. The ability to actually sit in or on something, move around your design, see it in space, and evaluate full scale will allow you to make better decisions and more fully understand your context. These can start very rough and become refined as you go. Any gained knowledge in the craft should be helpful in understanding and developing better design intent. This is not to say that you always need to be doing all the work and craft, but the better you understand it, the better your understanding of potential production methods and ways to make something can be, and this is what can give you greater control over your designs. I assume the process is different almost anywhere you work, but in general working fast and rough to discover and prototype quickly and being able to give clear direction on how you’d like to execute your design will take you a long way. The better you get, or understand any part of the process should only make you more well rounded and better.