I think it depends on the size of the pieces in the block. I'm doing a TON of double nine patch blocks that are finished size of 4.5" - each of the nine patch sections are only 1" finished. The degree of oops in these blocks is much different than the degree of oops in a 16" 5 or 7 patch. Additionally ... if it's a Bargello a little oops can be a big ICH!
Basically I eyeball it. Can I live with it? If not, I frog it.