Great God rookie seek advice android gravity sensor code problem!

Why gravity sensors to create a listener, but then again registered listeners and cancel listener, since record, and has been in the bad?
http://www.eoeandroid.com/forum.php?mod=viewthread&tid=70200

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Reply:
Because the sensor has a lot of it, so to specify the gravity listen, why do you want to cancel, I certainly do not want to cancel. Costs of electricity.
Reply:
Only registered not canceled, will be a memory leak.