Besides, try doing math or debugging some code without any conscious thoughts.
I agree most of the time it may be a broken record and useless, especially if you repeat the same patterns over and over again, but I'm quite certain you don't know what you are going to say until you've said it (out loud or not).
There is probably some miscommunication happening here. Do people regularly turn every intended action into a sentence in their mind? Like some kind of play-by-play sports commentary about their full life? I certainly do not do this, and I would expect most people do not.
I haven't introspected enough to know where I fall on that scale, but your example doesn't sound weird to me. If I'm home alone I'd probably say it out loud.
Putting your thoughts into words so that they can be understood by someone other than yourself or working through a problem are both deliberate ways of thinking that have clear benefits.
I do disagree with your last part. It's quite hard to test though. But let's say I'd ask you to just talk about any topic you want without preparing what you are going to say and right when you start a sentence I will randomly create some signal/noise which you should understand as the signal to stop talking immediately. I'd say you will know exactly what you were about to say.