The Parquet backend helped unlock traces search for large clusters (>400MB/s data ingestion) and over longer periods of time (>24h). It also helped unlock TraceQL (a query language for traces similar to PromQL/LogQL). There's more details in this blog post: https://grafana.com/blog/2023/02/01/new-in-grafana-tempo-2.0...

I don't have the exact CPU/bandwidth numbers on me right now but CPU usage has went up by about ~50% on our "Ingester" and "Compactor" components (you can read up about the architecture here - https://grafana.com/docs/tempo/latest/operations/architectur...). But this is optimising for read performance which improved significantly.