When purchasing new tires, the salesman is quick to recommend getting an alignment as well to prevent premature tire wear. I've even been told that you have to get the alignment done when the tires are new so they will allow the wheels to sit evenly and that worn tires will invalidate the alignment process since the wheels would then be "aligned" to the wear pattern.
In my head this seems to make sense because the wheels need to be aligned with the cars weight on the wheels to "set" the suspension, right? And if the wheels are resting on the ground (or the machine, whatever) wouldn't a very-unevenly-worn tire make the wheel crooked? Is this a real concern or is it a logical fallacy that the salesman is relying on?
Furthermore, is it really recommended that I get an alignment every time I get new tires? I've seen what a bad alignment can do to tires, so if the old ones are worn evenly, should I even bother?