It is definitely time consuming, but so worth it to have precut fabric when you need to make something fast. I use mostly 5" squares, 2.5" strips, and 2" squares. So I cut scraps according to what I use the most. I cut the strips and 5" squares first. The scraps that are left over get cut into 2" squares. Think about the shapes you use most often. Then cut the shapes you use the most, from large shapes to smaller ones.
I have a lot of dies, but I always cut scraps into the basic building blocks that I use for almost every project. I almost didn't start the scrap system because I was so overwhelmed by all the crazy shapes and variety of my pile of scraps. Now I am so thrilled when I get an idea or see a pattern and I already have the squares or strips cut. I can get to the project right away!