Yup, got one and use it all the time.;)
If you don't have one how would you ever know if you had acceptable runout in you necks, bullets etc. in you loaded rounds.
The gage, in itself, won't produce more accurate ammo but it will tell you when and if you have a problem and then you can track down the problem and fix it.
You will find that depending on the components used, the gun you have and the results you want, that your runout will probably vary in acceptable limits for different conditions.
For long range shooting the tighter you can hold the runouts the better off you will be to my way of thinking.