[Discussion] Streaming results to Client as they become available

Sometimes, the wait between “all tasks are done on the dashboard” and “.compute() returns” can be long (minutes) when computing large arrays (~60GiB), even with a local cluster. (Yes, I’m definitely oversubscribing my laptop in that case, but I’ve still generally found this type of latency noticeable in less-extreme situations.)

What is the historical reasoning for running `__dask_postcompute__` on the cluster and sending back one final concatenated result, instead of streaming each key/chunk back to the client as it completes, and doing the concatenation locally? If we were sending chunks back in parallel, I imagine we could hide that latency a bit, plus release some memory from workers sooner. Just wondering what the reasons are for not doing so.