I think that technically those are sedatives not anaesthetics, and might be used with numbing agents or nerve blockers just so that you're less aware of what's

I think that technically those are sedatives not anaesthetics, and might be used with numbing agents or nerve blockers just so that you're less aware of what's being done to you in cases where there's no need for a general anaesthetic. For example, my father needed surgery to his hand a few weeks ago - it's minor enough to have no need for general anaesthetics, so they injected a nerve blocking agent into the nerve to that arm under his arm pit and gave him a mild sedative. Or when I once needed a gastroscopy, I was given a sedative and a local numbing agent in my throat. As it is, doctors and surgeons would generally not put you under general anaesthetics if they have a choice. As soon as you're using general anaesthetics, you've significantly increased the risk to the patient and so it needs to be procedure that justifies the added risks. Frankly, there's plenty in medicine that we don't fully understand. However, for the risks that there might be some bad side effects the upside often more than make up for it. In this case, for the claimed 0.1% risk of having some level of awareness (a number which is refuted and more recent and wider ranging studies have put closer to 0.005% (or one in twenty thousand)), of which only a tiny percentage claim to have been aware enough to feel pain, the upside is that you can be treated for things which, pre-anaesthesia, you'd die of.