advantages of deactivation
The main advantage of deactivating RFID tags is that if I buy items in one shop, then I go into another with an RFID scanner on the checkout, if they have access tot eh database of tag codes, they will be able to correlate purchases of items in ther shop with other products, and if I pay with credit/debit/EFTPOS, then this enables them to build up a better picture of what I buy. This is a fairly small thing, but some people don't want everyone who cares to find out what I have bought.
One other advantage, which affects everyone, not just the tinfoil-hat brigade, is that if a criminal could use a portable scanner then they could identify people potnetially worth mugging by just walking past them, since even without the database of codes, most RFID-protected items are small or expensive, and that the carrier of many such items is likely to be worth robbing.