Speed absolutely matters. Of course if the quality is trash then it doesn't matter, but a model that's on par with Claude Sonnet 4 AND very speedy would be an absolute game changer in agentic coding. Right now you craft a prompt, hit send and then wait, and wait, and then wait some more, and after some time (anywhere from 30 seconds to minutes later) the agent finishes its job.
It's not long enough for you to context switch to something else, but long enough to be annoying and these wait times add up during the whole day.
It also discourages experimentation if you know that every prompt will potentially take multiple minutes to finish. If it instead finished in seconds then you could iterate faster. This would be especially valuable in the frontend world where you often tweak your UI code many times until you're satisfied with it.