Modo, you could use the X & Y coordinates to centre a design for in the hoop, the only problem is that you would need to know the X & Y coordinates for your machine. I don't use them in TrueSizer, I use my machine software to *place* the design, I find that much easier because my software has a button that says *centre design* - so simple! Personally I wouldn't bother with them in TrueSizer, if you don't have software, your machine should be able to centre a design for you. Hugs and a flower sweetie.
With X and Y you can change the position of the embroidery. They are the coordinates of the centre. Don't know what use it is in resizing, but filling in + or _ so many cm or inches just moves your embroidery around. *4U.