Force Pixel Alignment will snap vector objects, nodes and handles, and pixel selection areas to full pixels when created, moved or modified. If this option is off, objects and selections can occupy partial pixels.
Move By Whole Pixels
In addition to Force Pixel Alignment, the Move By Whole Pixels option allows you to constrain the movement of vector objects, nodes and handles to whole pixels.
Move By Whole Pixels is particularly useful for repositioning an object by a particular pixel distance while also maintaining the relevant partial pixels an object occupies.
To activate/deactivate Force Pixel Alignment:
Click Force Pixel Alignment on the Toolbar.
To activate/deactivate Move By Whole Pixels:
With Force Pixel Alignment active, click Move By Whole Pixels on the Toolbar.
To temporarily override snapping:
Press the while you're positioning. Snapping won't occur while the is depressed.