Cornering the grid puts all the leftover on two sides, so you print two spacer runs instead of four and lose less to rounding. Centering looks tidier and costs more parts.
Gridfinity standard — The standard Gridfinity base unit is 42 × 42 mm with a 0.5 mm wall clearance built into each module. Units tile at a 42 mm pitch. Wasted space shown is the remaining gap after filling complete units — it's split between both sides when centering. Measure your drawer's interior usable dimension (excluding rails, lips, or drawer slides).
The spacer plan — the print list comes from the MakerX Gridfinity Drawer Spacers: 12 widths (1.2, 2.4, 3.6, 4.8, 5, 10, 15, 20, 25, 30, 35 and 40 mm) in six lengths from one to six grid squares. The width engraved on a part is the gap it closes; its 0.4 mm lip adds another 10 mm that tucks under the baseplate, so the grid is held down rather than just boxed in. Sizes round down, never up — a spacer wider than the gap will not go in — which leaves at most 1.1 mm at the 42 mm pitch. The lip assumes a standard 4.65 mm baseplate; magnet or screw baseplates are taller and the spacer will sit low.