It may not be and it depends on the yarn fiber. Acrylics don't block, but a wash and dry evens out the stitches the way blocking does for wools. Since most of my knitting has been acrylic, I've never done it. I have a couple wooly scarves - one in entrelac, and one lacy that probably need it. Another reason to block is to get the size you need. I always knit the size I want, so don't have a problem. I also knit at a much looser gauge (on purpose, I don't like using anything smaller than 10s) which tends to make things stretchier than a denser knit.
sue- knitting heretic