Being unprepared heightens nerves.
Running through things because you are familiar with them, breeds routine and this is the seed of boredom.
You can sightread better if you know your scales and arpeggios.
Yes indeed I have gained a lot out of playing scales and etudes.
I use the traditional Moyse scale books slightly modified.
Never just run through a study because you happen to be familiar with it, but use it to see what you can get from it on this new day which has been granted you.