Snapping is a nice way to position an object with a set degree of precision. Here, we talk about the importance of snapping and discuss the various snapping types covered.
Placement snapping is snapping of position. It is handled similar to a 3-dimensional grid of points to which the user can snap.
Rotation snapping, also sometimes referred to as incremental rotation, allows you to rotate objects by a set amount.
Scale snapping allows a user to establish a set percentage of size change which can be applied to an object during scaling.
Vertex snapping is new as of Unity 3 and allows you to move an object to a particular object's vertices. It is very handy when you need precise placement for objects that are off the default 3D grid.