I square as I go ..... each piece is cut as straight/square as possible.
As each section and/or block is done, more squaring ....
...... making sure if it is to be 9" or 9-1/2" or 9-1/4", that it is.
If it is not.... what needs to be done for to fix it? and the subsequent blocks?
Then more of the same, before the borders are added, and with each border.
Then sandwich and quilt.
And yes, you guessed it .... a final squaring!
It really is not that much more work to do as I go along ... just part of the process, IMHO.
To me ... The final rewards of the finished quilt is more than worth that little extra effort!