I've registered the battery on my neighbors 5-series for him. As said above, it resets the countdown timer for battery replacement and changes slightly the charging profile. No big deal. Say you extend the life of that new $150 battery by 10% or 20% - you are saving maybe $30 over 5 years.

__________________
David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles