If you have an ARIN allocation, there is no reason you would ever want to decrease the amount of addresses you own. You own them.
The agreement you make to get an allocation requires a certain level of utilization depending on the size of the block to prevent squatting and exhaustion of resources. This is a good thing, and if it was actually respected we wouldn't be in a mad rush to migrate to IPv6.
it only took 20 years to standardize after all. we're seriously rushing here!