Its kinda silly it needs to lack resources to work, rather than just be unable to work (either lack of resources or no recipe set)
The problem with this AP Adv is that it needs some mechanism of control currently not present. You're right that it should be able to start on its own, not wait for an insufficiency - but it also needs some kind of "stop" criteria, or "don't progress to this" criteria, to avoid completely consuming valuable resources needed for other purposes.
If a smelter or crafter is unable to work due to lack of resources, 120 minutes later this will automatically change its recipe to the most expensive recipe that it can work on. Upgradable to 10 minutes in -10 increments. Can be enabled or disabled at will.
So for example if you're saving up for Gold bars with needs Tin ore, or Titanium bars that needs Silver ore, or Thorium bars which need Zinc orc (and same for Chromium/Neodymium/Samarium/Lanthanum/Unobtanium/etc) which each need more of the 'cheaper' ore than the native alloy bar itself, could be starved to never complete if the "most expensive recipe" uses up all the ore.
So let's say you try to create a Titanium bar, and you have 4 hrs Idle time, and you calculate that in 3 hrs, you'll have enough Titanium ore, so when you come back in 4 hrs, you'll have a Titanium bar. Auto-smelt will actually kick in after 120 mins of not having enough Titanium ore, and could start smelting Silver bars (if it's the most expensive bar you're able to smelt) and use up all the silver ore. Thus, you'll never make Titanium in this case, and having spent AP for Auto-smelting could actually hamper your play. And "upgrading" this AP Adv just moves this danger forward in time, so bad things could start happening in less than 120 mins of starved smelters.