When you said "milling", I also thought you meant slicing and dicing logs.
Yes, I generally prepare all my material from rough sawn or skip planed material. It's more economical to buy rough and lightly skip planed lumber and by jointing it flat and thicknessing myself, I have absolute control of things like grain match, figure and color, thickness, etc. I'm a firm believer that selecting the material is the very first step in the finishing process and doing a good job there can take a project from "that's nice" to "wow!". I also prefer to work in the thicknesses that are appropriate for my project, not the thicknesses that are on the rack at some supplier. Proportion is everything sometimes. (I've moved to metric, too) And having someone else joint/plane for you will almost never result in the same quality you will get with your own tools if you become skilled at the task, despite the time it takes to do it.
That said, if you do basic projects that can work with commonly available thicknesses and "quality of flat" you might get from a supplier, there's no harm in simplifying your life.
If it makes you feel any better...I've barely touched my lathe in something like 8 years. I'd not give it up as it's a very capable machine for when I want or need it and I wouldn't get close to it's value in resale. (Stubby 750) I'm hoping to get back to turning a little going forward, even if it's small things for other kinds of projects.
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The most expensive tool is the one you buy "cheaply" and often...