I like to make my quilts one block at a time because If I made a mistake in cutting or color choice it shows up in the first few blocks and I can then make adjustments with out having cut a whole quilt wrong or used wrong colors.
Sometimes it helps me decide if I actually like making the block. By doing them one at a time there is less time spent on discovering all these things and alows me to enjoy the quilt making as it grows row by row.
peace.