system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some helicopters have two rotor blades and others have four ? And what exactly are the benefits of each type?

I've always wondered that.
gpt
How much wing you need to lift how much weight with how much engine. Each blade is extra weight and extra torque you need from your engine. The upside is that each extra blade gives you more area to generate lift and speed. So it's a balance between the two.