Usually, resizing in draw.io works in 10-pt steps (meaning one step of the grid equals 10 pt). But sometimes you want to paint with a finer brush, so to speak. With this shortcut, you can resize your shapes down to a 1 pt level.
I know. Even we can’t believe it sometimes.
All you have to do is click on the shape resizing points, hold the mouse button, and hit the Alt key. Now the shape is no longer bound to the grid, and you can change the size of your shape pixel by teeny-tiny pixel. And if you hit Alt+Shift, you can have it both pixel-perfect and centered.