With Snap Frames, all key and range bar positions that are changed are forced to absolute frame increments. This includes selection sets of multiple keys. When Snap Frames is on, each key in a selection set will snap to the nearest frame when the selection is moved or scaled. Default=on.
When you use the Time Display format MM:SS:Ticks, which doesn't use frames, Snap Frames snaps to time values that match frame boundaries.
In Dope Sheet Edit Keys mode, keys are displayed as a box grid. Keys that are snapped to frames are displayed as filled boxes. Keys that have been moved with snap frames off are displayed as narrow rectangles within the grid. When using the Curve Editor, a similar display is available in the track bar.
Subframe keys moved with snap frame off
Snap Frames is on by default, so the following procedure only applies if you have turned off snap frames previously.
With Snap Frames on, each key in a selection set snaps to the nearest frame when the selection is moved or scaled.