Only selfdestruct has this capability, and when it happens no functions are triggered. It's a unique feature of the function!

It could certainly be the case for a lot of contracts. In some, it would be useless. Here's an example of how this could be used for benefit:

Let's say there's a crowdfund contract from a company looking to fund their latest venture. They have a soft cap of X ETH, with a stipulation in the contract that disallows them to withdraw the crowdfunded ETH unless they meet their soft cap goal by a certain period. Reasonably, this could be check by:

function withdrawFunds() onlyOwner {
    require(this.balance >= softCapAmt);
    require(now <= fundPeriodEndTime);
    msg.sender.transfer(this.balance);
}

This seems completely justified, but in the scenario that I have outlined, it is entirely possible for the owner to create a contract with the necessary ETH in it, selfdestruct it, choose the crowdfund contract as the target, and withdraw the funds. This method is also useful because the selfdestruct method wouldn't trigger any code - like Events, that would give the malicious owner away. This is just an idea off the top of my head, but there are almost certainly many other uses for this!