LoRa spreading factors are often misunderstood as simple range-versus-speed knobs. The real behavior depends on physics, airtime limits, collision domains, and regulatory duty cycles. Higher SF values increase symbol duration and processing gain, which improves sensitivity but dramatically inflates packet airtime. This has three key consequences: longer transmissions, higher collision probability, and stricter duty-cycle impacts.

The common belief that higher spreading factors boost throughput is incorrect. They increase packet duration and duty cycle occupation, reducing usable channel capacity. For example, an SF7 packet might occupy a channel for tens of milliseconds, while an SF12 packet can take multiple seconds. This scaling effect collapses capacity as traffic grows, especially in mesh networks.

LoRa's shared medium means one transmission blocks others on the same channel. In simple star networks, this is manageable, but multi-hop meshes face design constraints. High SFs become throughput choke points, not performance enhancers. Regulatory duty-cycle limits in Europe (ETSI) and the US (FCC) further restrict airtime, making careful SF planning essential for real-world deployments.