And as for why you might want to spawn processes in these cases - it helps isolate memory corruption, other unrecoverable process failures, or even just issues like memory fragmentation to a specific unit test / file build - so that issues building/testing X don't show up as intermitent failures that get misattributed to building/testing Y.

As a workaround for perf issues like the article, you might choose to reuse the same process more instead, but it's a tradeoff.