When you move or edit images and boxes in iWork, 'snap to grid' function can be very helpful – objects quickly jump to align themselves with the layout grid or with other objects.
In a design where there are numerous objects it can be maddening. Objects align with the layout grid and with other objects.
To disable this function, press Command after starting to move objects or dragg their handles. Remember, after, not before, otherwise a different function – rotating – activates.
Apple doesn't actually use the term 'snap to grid'. Instead, we have Alignment Guides in iWork.
If your design requires moving and editing numerous objects, disable Alignment Guides. Under Application menu (Keynote/Pages/Numbers) open Preferences>General and uncheck the boxes 'Show guides...' under Alignment Guides. The menu says 'Show' but in fact means activate or disable the snap to grid function.