A simple analogy
Closed models are professional kitchen appliances you rent by the hour. Open models are the same-grade equipment you buy, install, and maintain yourself. Renting is easier; owning is cheaper at high volume but requires your own expertise.
What it looks like in practice
A healthcare company needs AI that never sends patient data outside their private cloud. They deploy an open-weight model on-premise, accepting higher infrastructure cost in exchange for full data control.
When to use it
Closed models are right for most teams starting out. Open models become compelling when data residency is a hard requirement, when volume makes per-token pricing uneconomical, or when you need to modify the model itself.
When to avoid it
Do not choose open models to save money early. The infrastructure, operations, and expertise costs easily exceed closed-model pricing until you reach significant and stable volume.