I've been thinking about this a bit recently, and the saying should be extended to "I've got nothing to hide, now." Things change and either you'll do something which you'll want to hide, or society/politics/community will change which you'll have something to hide.

An example in the first case is that you'll want to buy a secret gift for someone, but because of the tracking the surprise will be spoiled because they'll be seeing ads for it on their systems.