VNAV PATH works well if all the info you put into the computer is perfect. If you put in forecast winds for your descent, ISA deviation, landing QNH etc. then the thrust levers close at TOD and don't open again until you level off at your end of descent waypoint.
If however you cockup the winds, or as I heard happened to a friend of mine, the FO put in the wind 180 degrees out at 100kts, you can either end up really high or really low.
If you end up high the a/c will nose over and hit VMO/MMO and go initially DRAG REQUIRED, ie use the speedbrake, and then if your still high, OVERSPEED DISCONNECT, and drops you into level change. Its then up to you to get down in so much as the a/c can't do any more for you with the automatics.
If you get low on the projected path, it will allow airspeed to drop to target minus 15kts then will add power to maintain approx 1000fpm until flying back into the path when it will reclose the thrust levers and try again to go down with them closed.
Thats about it.