It depends on the problem domain you have and the way you prompt things. Basically the reasoning is better, in cases where using the same model to critique itself in multiple turns would be better.
With code, for example, if a single shot without reasoning would have hallucinating a package or not conformed to the rest of the project style. Then you ask the llm check. Then ask it to revise itself to fix the issue. If the base model can do that - then turning on reasoning, basically allows it to self check for the self-correctable features.
When generating content, you can ask it to consider or produce intermediate deliverables like summaries of input documents that it then synthesizes into the whole. With reasoning on, it can do the intermediate steps and then use that.
The main advantage is that the system is autonomously figuring out a bunch of intermediate steps and working through it. Again no better than it probably could do with some guidance on multiple interactions - but that itself is a big productivity benefit. The second gen (or really 1.5 gen) reasoning models also seem to have been trained on enough reasoning traces that they are starting to know about additional factors to consider so the reasoning loop is tighter.
With code, for example, if a single shot without reasoning would have hallucinating a package or not conformed to the rest of the project style. Then you ask the llm check. Then ask it to revise itself to fix the issue. If the base model can do that - then turning on reasoning, basically allows it to self check for the self-correctable features.
When generating content, you can ask it to consider or produce intermediate deliverables like summaries of input documents that it then synthesizes into the whole. With reasoning on, it can do the intermediate steps and then use that.
The main advantage is that the system is autonomously figuring out a bunch of intermediate steps and working through it. Again no better than it probably could do with some guidance on multiple interactions - but that itself is a big productivity benefit. The second gen (or really 1.5 gen) reasoning models also seem to have been trained on enough reasoning traces that they are starting to know about additional factors to consider so the reasoning loop is tighter.