Comment by kubectl_h

You have to do the tracing anyway if you are going to sample based on criteria that isn't available at the beginning of the trace (like an error that occurs later in the request) and tail sample. You can head sample of course, but that's going to be the most coarse sampling you can do and you can't sample based on anything but the initial conditions of the trace.

What we have started doing is still tracing every unit of work, but deciding at the root span the level of instrumentation fidelity we want for the trace based on the initial conditions. Spans are still generated in the lifecycle of the trace, but we discard them at the processor level (before they are batched and sent to the collector) unless they have errors on them or the trace has been marked as "full fidelity".