In my third year of quilting I joined a couple of online groups and was really into block swaps. All the blocks up to that point were to be 12 1/2 inches. I put a lot of effort into making sure they came out at 12 1/2 inches and beautifully pressed. Then I folded them up and sent them off. I made some cyber friends along the way and when I received their blocks back I noticed that there was a lot of "tolerance". Because I was still kind of new to quilting and didn't trust myself to "fudge" the end product, some of those swap blocks I received I ripped out and remade. The kill point for swaps for me was trying to make the perfect 3.5 inch nine patch. I put in hours to make them come out right. I had lots and lots to make, got lots and lots back with lots and lots of "tolerance". So I guess the bottom line is how much time do you want to spend making sure your blocks won't make your quilt grow out of proportion? If it is not as important or you know you can adjust with sashings then the tolerance factor isn't really an issue for you. But it may be a huge issue for someone else receiving those blocks.
Heidi