Having many colors and many fabrics in a presentation has a few drawbacks. One is that as a designer, you want to have a cohesive theme or "look," something that differentiates you from others. Too many fabrics and too many materials detract from that effect. Another is that too many fabrics and colors can distract visually and in a tactile way from the strength and beauty of your work. If there is too much going on, the eye and the hand do not know where to start. Sensory overload floods the senses, so that nothing stands out in particular, and sensory overload often leads to your audience just shutting down. Strive for simplicity in presentation, with a strong theme and a few fabrics and colors that work well together. Your work will be far more impressive and memorable.