[Kevin Kolodziej]

One thing FIRST might have overlooked:

The bar can be lowered after a match so that robots can be removed easily. If you have just a hook, you can lift your robot straight up and carry it (which will be very awkward) off the field. Then you can tether and lower it to fit through doorways and such. If you have a locking mechanism on your hook so that you can't be knocked off the bar (a simple spring latch), you can't reach it to open the latch and lift your robot. The bar is lowered to where you can reach it...but if your robot is only a couple of inches off the ground, that bar can't be lowered more than a couple inches. The whole system would get jammed and either ruin the mechanism, the robot, or both.
The simple solution is to swing your robot around the bar so the bar can be lowered - this will take at least three people per robot (two to hold the robot steady, one to release the mechanism and catch that half of the robot) which is not a big deal. If there are 4 bots on the bar and on top of one another in a big mess, this is going to take time to sort out and get taken care of. Here is where the problem comes in. If your robot is only off the ground an inch or so, there will most likely (depending on the position of the hook relative to the robot - edge or middle) not be enough rrom to swing your robot clear of the platform. If there is one bot like that, there could be other bots stuck 3' off the ground. Now we have to find ladders and take great care not to fall off the ladder, not to get crushed by the robot, and whole mess of other things. I'd say this situation won't be common, but you never know.

NOTE TO FIRST: Have ladders on hand at the arena!