When I do a tension square, I do it as quickly as possible, get close enough and think "that'll do" because I want to get on with the actual making. I'm never properly happy with the fit of anything I make though.
I've read recently that you should knit the tension square and then properly block it before you start the project so you can be sure of the gauge.
Does anyone actually do that and does it make a difference to the end result?