It's sometimes useful, it seems. But when and why it helps is unclear and understudied, and the text produced in the "reasoning trace" doesn't necessarily correspond to or predict the text produced in the main response (which, of course, actual reasoning would).

Boosters will often retreat to "I don't care if the thing actually thinks", but the whole industry is trading on anthropomorphic notions like "intelligence", "reasoning", "thinking", "expertise", even "hallucination", etc., in order to drive the engine of the hype train.

The massive amounts of capital wouldn't be here without all that.