To all those who are indifferent about the backups, just don't worry about them and you'll be fine. The RC still runs off of the main battery, and a lot of teams will never have to worry.
To us, they are a godsend, considering the current draw our robot has. Two years ago, when we tried six motor drive for the first time, lack of a backup battery was one of two major setbacks; this lack of available power would cut out our RC in pushing matches. In 2003, they fixed the other problem with the nice 120 amp breakers we take for granted (which used to sometimes pop when we stalled our gearbox). Finally this year the second problem was fixed and we no longer have to worry about our
RC cutting out after too much pushing.
In the end, there's nothing really that should make you unhappy with the backup batteries; either they are very useful, or they are neither bad nor good.