It's best to use sizes that you can mange and carry about without too much trouble. If your boxes are too big, they become unwieldy or too heavy to bear. They will be anchors instead of useful tools.
They are finite in size so only so much can fit in them. When you get to the top, you have to start putting stuff in new boxes. This forces you to focus on only what's contained within them.
You can label them, color code them, stack them, put them away for later.
I imagine boxes in my mind and I can be still.
