This ensures that all of the work gets done, but it can mean that performance is impacted at peak times.
You pay only for what you use, with per-second billing and also accumulate one hour of concurrency scaling cluster credits every 24 hours while your main cluster is running.
Concurrency Scaling Clusters are used to handle many forms of read-only queries, with additional flexibility in the works; read about Concurrency Scaling to learn more.
The Concurrency Scaling Usage shows me how many seconds of additional processing power I have consumed (as I noted earlier, each cluster accumulates a full hour of concurrency credits every 24 hours).
I can use the parameter max_concurrency_scaling_clusters to control the number of Concurrency Scaling Clusters that can be used (the default limit is 10, but you can request an increase if you need more).