It's the single most important aspect of writing daily. Actual production ranks right up there, but momentum is what keeps you going and keeps you involved.
Even if you re-read the last scene you wrote yesterday and have only 15 minutes to write today, those extra sentences--or that paragraph or three--put your mind right back into your project and propel you forward. Even if what you wrote yesterday was garbage, and today's efforts just make the pile bigger, you're more in tune with what you shouldn't be doing--which is the first step toward figuring out what the heck you should be doing.
I wonder how YOU benefit from writing daily...