For me it depends on what the project is. I do pinwheel baby quilts and I don't square up anything. I make the centers match and don't worry about the outside edges too much. You can fudge a whole lot and as long as the centers match up fairly well, by the time it's quilted and washed you don't really see the imperfections anymore. The moms don't see them and the babies don't care.
But if the quilt is going to be much bigger than a baby quilt size those imperfections add up to a mess by the time it gets to be queen size.