It is generally worth it, so long as nothing happens to your device and you're actually getting a deal. Phone contracts where you're getting hundreds off the price of the phone? Sure I can see the appeal so long as the plan they require is well priced for your needs. But should anything happen to your phone? Tough tit. You're still paying every month and you have to buy a new one. The damage may not even be your fault for that matter. The phone may have simply died after the warranty expired. More companies are offering early upgrade options now so it's less of a problem (because they literally bleed customers when this sort of stuff happens. Tell a person they have to pay full price to replace their phone and they will pay the cancellation fee just to get a free phone somewhere else and tell you to suck it more often than not), though if they're just tacking another 2-3 year contract onto your existing contract you're getting ripped off.
You don't have to be irresponsible to not be able to pay your bills on time. "I'm sorry you lost your job and can't afford this phone and contract anymore sir, just pay the $200-300 cancellation fee and all of your outstanding bills and you'll never hear from us again."But then, I'm not an irresponsible individual who won't pay my bills, nor have I ever been.
I'd have less of a problem with service contracts for electronics if they didn't leave customers completely and utterly at the mercy of corporations with better lawyers than you could hire, even if pursuing legal action made any economic sense for an individual.