Why do we do scales? For many adults that attended music lessons in their youth, they will tell you it was a torturous device that us music teachers give. They will say that it is just busy work. That is not the case. I am here to tell you that there is another purpose and it helps all instrumentalists including vocalists. So here it goes!
First, lets take the very simple scale in whatever key (cause it doesn't really matter). Once you learn the framework of where your fingers go and what notes correspond with each finger, now you know where that note is each time you see it in music. Your fingers are now going to automatically go to that fingering out of pure muscle memory. You have now connected your brain and fingers with reading on the simplest scale because it is just one finger after the other and in musical alphabetical order.
Now if you play a bowed instrument the next step is to use that muscle memory to your advantage and now focus on how well your bow is moving. You can play a set of notes and not have to try and memorize a pattern of notes to work on your bowing. Trust me, if you have to learn a new song and work on the bowing together...something is going to be lacking at some point and you won't learn the song as fast as you like with the proper technique to make it sound right. It just won't happen for you the way you want. Trying to learn two movements at one time is tough so just make it easier on your brain and practice your bow movement on a scale that is so simple and easy.
If you are a vocalist, the same is going to apply. Practice your breathing and note control on a simple scale.
Now if you are going for a little more advanced scale you are expanding your everything. Whether you are a vocalist or an instrumentalist you will be expanding your skill and range. You may be learning new notes that go beyond the musical staff (that thingy that has five lines and holds all of those dots with lines attached to them) and learning how to get to them. Practicing how to get to these expanded range notes ahead of time makes it that much simpler when you see these notes in your music and need to figure out first what that note is, second, how to get there and play it and third, what that note is really supposed to sound like.
For a vocalist, using scales will help you exercise your voice to sing in different keys and ranges. You can also use the scales as a measuring device to see how far you can get in your range and help you exercise your voice to extend it.
Piano players. Doing scales is to improve your proficiency at moving up and down the piano as well. Exercising fingers to make them stronger and more accurate. It will also get you thinking in patterns of movement and get you feeling the space between different notes in different types of scales so that you can feel your way across the keyboard and not have to look too often.
Now you've really learned your scale, you've improved getting up and down (even if it was a more advanced scale), and you have improved your skill range that much more. Now you can take that scale and do some improvising over some chords or over one of your favorite recorded songs in the same key. Use that scale to now construct a song yourself. Put it in different patterns and see if you can get your fingers or voice to survive through patten twisters (that is all an etude really is.) Just have fun with it! There is no need for a scale to suck the life out of you. It will help you in the long run and will improve your skill that much more. So scale the wall and see that there is so much more to do than just feel bored out of your mind.