Yes and no, it depends on the fabric as I have had some (yes the good LGS fabric) stretch when I iron and I know to press not iron (sliding the iron). On those I ease in leting the feed dogs do the work as they will shrink back to the right size after the finshed quilt is washed. It always seems it in the corner where it stretches and I know if I square up the block I will be losing that required amount of threads. I haven't had a problem with the tops or quilting when it's been a problem with the stretching and easing it in. Once the top is sewn together and reironed before quilting they seem to fit in sort of unstretch if that makes sense.
I'm am careful with my cuting and sewing the 1/4" so my finshed block are the finshed size they were to be.