I love to fussy cut when it is needed because I am one of those who likes to see the whole character/flower if I am paying for it. Fussy cut square makes the quilt pop.
I have the fussy cut squares but frequently I need a different size. If I don't have the right size, I take tape and use it to mark a square the size I need -- if I start in a corner I only need to tape 2 sides (be sure and include your seam allowance). I also use a washable marker to mark the exact center of the square so I know where to place the ruler for cutting (or marking the square for scissor cutting, depending on how my hands feel).