I guess to an average onlooker Fashion Design is all about Design and Design only.
However, lets take a look at Fashion Design from a larger perspective. Fashion Design in reality is not about coming up with the wildest and most creative ideas. It is also about improving a product to make it as flattering and desirable to wear. The most successful fashion designers are those who are practical. That’s when the sewing angle comes in. Sewing in fact is a very huge part of fashion designing, because if the garment is not sewed together you don’t have a finished product.
In other words, it is not the question of sewing being necessary or not. To be good at something you need to have added skills to make your profession complete. A good fashion designer needs the clients to be able to understand their design. Sometimes just talking about the product is not enough. If the designer knows how to sew then it is a great way to make sure the design is understood. This helps avoid delay in making the prototype too. Sewing in fact is really the best way to convert your visual product into becoming a finished product.
Likewise a good fashion designer also needs to know about fabric. The choice of fabric in design helps to enhance design and reach the effect a designer has in mind.
So basically if one is interested in being a fashion designer and the best one at that, it is important for you to have knowledge of sewing. This will be a great asset in your profession as you will discover on your own.