The "need" to square up or block a unit to make it the correct/expected size
If the fabrics have been washed before cutting, the cutting is accurate, and the seam allowances are the right size/consistent, in my opinion, there should be little need for squaring up or blocking a unit. It should come in pretty close to the expected size.
I am definitely opposed to "stretching" a block to make it bigger. It will just revert back to whatever size it was the next time it is washed.
If I am expecting to get a 12-1/2 inch unfinished block and it is more than 1/4 inch off, I will remake it. My personal "fudge factor" is closer to 1/8 inch.
What is your "fudge/slop factor" tolerance?
There are some blocks - that can "tolerate" a lot of trimming to make them the same size. Others are more finicky.