You can do head-based sampling and tail-based sampling. With head sampling, the first service in the request chain can make the decision about whether to trace

You can do head-based sampling and tail-based sampling. With head sampling, the first service in the request chain can make the decision about whether to trace, which can reduce tracing overhead on services further down. With tail-based sampling, the tracing backend can make a determination about whether to persist the trace after the trace has been collected. This has tracing overheads, but allows you to make decisions like “always keep errors”.