I usually cut the pieces for one block and then assemble it. Then I will cut the rest of the pieces for the whole quilt. Many of the quilts I've made lately, while they are not scrappy, use a variety of fabrics, meaning each block may be unique. I always cut and lay out the fabric pieces for each block so I don't end up with blocks at the end having poorly coordinated fabrics. If I have many blocks, I pin them in sets of 10 also.