For a very long time, I've believed in the idea of quality over quantity. But recently, I've had to look at that idea again. If taken too seriously, this can result in not doing anything or not finishing anything. It comes with perfectionism; the thought of "It's not done until I make these little improvements" can be never-ending. But finishing things and moving on to new things is the best way to see your improvement. Now I'm not saying that quantity over quality is the answer either. I think there needs to be a balance between the two.
Putting quality first can be a good strategy when sending something to your boss or the public. You should always put your best foot forward and try to do your best work. In doing this, you wouldn't work on many projects since quantity isn't essential. You probably shouldn't post everything you create or send in something without checking and editing. Always proofread your emails, people.
But, you need to recognize when something is your best work when you've gone back and edited it to your liking. Here's a trick, If you made an edit that you change later and then change again, it's time to move on. You should only change the same part of your song, sentence, or phrase once or twice. This, of course, doesn't apply changes that need to be made to fix things. If you're a coder, and your program doesn't work, make as many changes as you need :).
If you're putting quantity first, this could hurt you if your work isn't as good. But this only applies to work that is being shown to represent you. So, it shouldn't be everything, but it should be a lot. This means you have to create much more than you plan to share. Make a lot and pick what's best.
Your first priority with your work doesn't have to be your only focus. It isn't quality over quantity or quantity over quality. A balance of both is the best way, at least in my opinion.