In the short term, this is actually bad for your credit score (ah the irony), so don't do this in preparation for any planned major investments that require a credit check.

Better option: don't open a bunch of arbitrary accounts in the first place. Weigh the benefits of special financing offers carefully and determine if it's actually worth it to get 0% interest for 3 months on the purchase of a TV in the long run.

Regarding identity theft, if they are truly unused, said credit cards are only a minor threat unless the security of the given financial institution is inferior. Most credit card theft occurs after the point of purchase either in person or online. Full-blown identity theft would require the aforementioned bank security breach or the actions of a dishonest friend or family member since access to a credit card number itself doesn't provide access to social security number and other information required to open other accounts.

This is a good idea for improving your credit score too, for those who care about such things. The more credit you have out there, the less attractive you're going to look when you try to buy a house or something else huge. You'd hate to have that fashion bug card cost you your dream home, wouldn't you?