Of course 5W-30 is just the default recommendation (and not a bad one). You can (and perhaps should in some cases, but do your homework first) pick other weights to protect the engine better depending on your ambient conditions and driving style. Going thinner (lower numbers) protects you a little better from cold-start wear, so it's a good idea in very cold weather, or if you're doing lots of engine starts per mile (many short trips turning the car off between), whereas going thicker will maintain viscosity at high engine oil temps better for when you're racing. It's all a tradeoff, there's no universal answer that's best for all scenarios.
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