I'm a bit in the minority it seems. I figure out the math and then cut the right amount of strips, then squares. I prefer to sew in an assembly line style. It's slow to see progress but then when the blocks are done they are all done at the same time and I feel so accomplished. I use to just make a random amounts of blocks and then when I have to cut more pieces I would get annoyed and avoid it - cutting the pieces is my least favourite part. I would make less blocks then I needed and just added a few borders to make it bigger and always regret it. Sewing enough blocks from the beginning means I don't have to have a big border, which is my preference.
I think if I was doing a more complicated block I would do a block first, and then cut everything