You want to get a lot of words on the page when you're working. You want those words to be good and you want them to be the right words. Move the story forward. Develop character. Move at the pace you want. Make your reader feel what you want them to feel.
You've got to stay in the flow. Do that and you will write better and faster.
This is both easier and harder than it sounds. If you are in the flow, the words are, well, flowing, and you're doing all the things you want to do. Nothing can stop you. Except an interruption. And here's the thing, often that interruption comes from us. We can talk about the psychology some other time but I know, from personal experience, that sometimes I will give into various interruptions: I must check my email, google some information, do research on my story, walk the dog, talk to the dog, play with the dog (blame the dog for wanting me to play with the dog). You name it, I've probably used it as an excuse to wander from the act of writing. Take a little break. That's a common one.
The thing is these breaks do, in fact, break the flow. They're a scourge on writers. Not just because it takes time to get back into your writing (it does, always) but because it breaks connections we were making when we were in the flow.
It's simple. Build better habits. Be aware. Be mindful of when you take a break and why. Most of the time it will just be an excuse. And it will harm both your writing and your output. When you're writing make yourself actually write. Don't waste the flow. I fight this all the time because I'm prone to daydreaming and distractions. But I'm much more aware of how much time this wastes now. So, may the flow be with you, writing brothers and sisters.