Well, I guess I'm the exception. I turn (at least a cleanup) on everything I shoot except for 223 plinkers in an AR. I've used a forster tool before, but now I use K&M turner and their matching expand-iron. Henry, you can get an expander pretty cheap SInclair international, but I really like the K&M - the attachment of the mandrel to the base is a better design than the ones that use a set screw on the shaft of the expander, and the taper along the shaft is at a better angle for smoother expanding.

I usually start the process on once-fired brass, and run it into the sizing die withe the expander ball removed. That way the case will be about as concentric as you can make it before you expand the neck, and the neck/shoulder junction will be at the desired location on the case. Then I lube the neck with Imperial wax and expand it. Then I turn it. You need a pretty close fit between the ID of the case and the turning pilot. If it's too loose, you can turn a little off of the expander mandrel by chucking it in a drill and rotating against oiled 400 grit wet/dry emory paper. Once you have a good fit, polish the shaft with Flitz s and it will minimize rusting and make the tool function better.

I usually set the turner "loose" and then gradually tighten it until it "cleans up" about 75-80% of the neck circumference. Try a few test cases and you'll see what I mean. On some cases/calibers, I turn to a specific diameter to eliminate almost all case neck variability. It can have an effect on concentricity, which in turn improves accuracy, but you may get more mileage out of other practices first. You may need to buy a tubing mircometer to see how "bad" you cases are to start with - but be warned, once you start measuring them, it's hard to ignore the variability you see expressed in the measurements.

I do it because it's something I can do to control variability, and the more I shoot the more attention I pay to the case necks. Having the necks uniform is worth the effort for me.
ELkbane