Your Nissan 350Z or 370Z isn't just the average car down the street. They are exceptional machines and earn the respect and adoration of their owners. You don't want to risk the integrity of your vehicle with some shoddy aftermarket parts by some shady company. So, when you want to repair or customize your vehicle, you could run into problems getting parts. Buying from the dealer is expensive and a lot of times they don't carry the parts in stock. Some aftermarket products might not be available through them. Ordering from Japan can take a long time and be expensive in regards to shipping. The local parts store probably doesn't stock everything you need.