I put grey-scale lines on the essay page for the most recent exam I gave to my classes, and, to a student, everyone wrote more neatly and organized their ideas more successfully than they did on the essay portion of their previous exam, where they only had margin-less space on a blank sheet of paper.
Perhaps having margins and guidelines helps to alleviate the feeling of working in an abyss, particularly when there is potential tension involved.
While I was practicing Brahms this evening, I noticed, after recording and playing back a passage or two, that I was not always holding notes out quite as long as they should be held. Sure, I was counting quarter notes, but something was amiss. I decided to practice with the quarter notes on off beats (the beats-per-minute wheel on my old-school metronome doesn't go high enough to subdivide the quarter notes into eighth notes in a fast tempo), and after half an hour of actively and deliberately subdividing every single beat, and then re-recording and playing back the passages that bothered me earlier in the evening, I found that my rhythm was much more satisfactory. I also played with cleaner articulation, and found there there was more "voltage" happening during long notes. I even found that I could use rubato, and snap back into tempo whenever I wanted to.
It's kind of like having margins and guidelines. The margins and guidelines on a piece of paper do not put creativity in any kind of straitjacket, and neither does subdividing beats when playing Brahms. It might even alleviate tension, because exactly "when" to play is no longer a question. It becomes an answer.