Where Expected Size May Not End Up Being Expected Size
This is a spin-off from scant or full quarter inch seam thread -
Ruler placement - are your cut pieces "exact"? If cutting around a template, my pieces are a smidge larger than the template.
When cutting strips, they are also a "smidge" wider than what I think I am cutting.
Example: my 2-1/2 inch strips are probably 2-1/2 plus 1/32 inch.
I don't have a die cutter - so I don't know about how those work, nor have I used my strip cutting ruler. I also don't know how wide jelly rolls actually are.
Seam width - discussed a lot
Pressing - if using unwashed fabric and using steam to press - there can be shrinkage. Also, if there is a bit of a tuck/pleat left by the seams. I press the seam line so the stitches almost show. One can also stretch the fabric if one gets overly exuberant while ironing the piece. Ironing a piece like rolling out pie crust may not be recommended. Although I have done so and my pieces are fine.
All these things are cumulative.
I was aghast that Sharon Schamber was advocating stretching a block that was too small. What happens the next time it is washed?
So - most of us have learned what works for us. I will trim HST's to size. So far, if I cut the square +7/8 inch and sew with a VERY scant seam, they end up skimpy. So now I cut my squares + 1 inch and still sew scant 1/4 inch seams and they usually are barely okay.