Grid mode, where cursor placement and region moves are constrained to a grid, is invaluable for moving sections of a song without losing the musical timing. It's also great for building rhythm tracks and other sections while being sure that elements fall on the beat (or within the beat in a musically congruous manner, such as every eighth note, or every 1/16th-note triplet).

As I've said, any available time ruler -- selected in the Grid pop-up, on the top right of the Edit window -- can be used as the grid reference. When working on a song, you'll probably select bars:beats as the reference, and, for instance, a quarter-note grid resolution (there's a broad choice of resolutions, from a whole note to 1/64th note, with options for dotted and triplet values). It's possible to make the Grid appear as vertical lines in the Edit window, which is helpful and reassuring -- seeing those kick drums neatly aligned to beat lines is comforting.

Another Grid editing option is well worth mentioning: If you select Region/Markers as a reference, edits or cursor moves will align to the boundaries of regions residing on other tracks, or to markers inserted in the timeline. This option makes it easy, when working to picture, to trigger sound effects with MIDI notes matching markers corresponding to specific timecode locations, or to precisely align MIDI notes to non-quantized audio regions, which is great if you need to beef up live recorded drums with MIDI-based sounds. The missing step would be the ability to extract a tempo map from such a MIDI track, so that the bars:beats grid followed the audio accurately -- maybe in an future update?

By setting the grid to Regions/Markers, event moves in Grid mode are constrained to existing region boundaries. In this example, I can very precisely augment two audio drum tracks with perfectly aligned MIDI notes.

Also, while I'm wish-listing, it would be nice to have a "proportional" option for grid editing; for instance, when moving a region a bar away from 1/1/034, you may want it to snap to 2/1/034 instead of 2/1/000. For now, there are two ways around this: the new Shift command, which applies a positive or negative offset of any value to the selected events, or the Nudge command, which does that one step at a time. The Nudge pop-up menu, located just under the Grid pop-up menu, lets you choose a separate timescale and resolution. This allows you to edit musical events to a bars:beats grid while at the same time being able to nudge a vocal take by ten or 100 milliseconds so that it sits better in the track.