Neck Turning

Starting with quality brass is probably one of the single best things one can do for improving your accuracy when sound reloading practices are followed.
I try and use Lapua brass for every caliber i own if it's available but there are other great choices out there Nosler/Norma, Alpha, Petterson to name a few.
Many feel that Lapua brass does not need neck turned due to its level of uniformity straight from the box but the necks do run on the tight side and it's beneficial to run them through a mandrel before loading.
I personally prefer to neck turn my brass even Lapua but I usually just take a clean up pass that has 85-90% clean up to remove any variation in thickness while turning just enough into the neck shoulder junction to help prevent the formation of a donut.
If you are not running a tight neck chamber it really isn't necessary but the more consistent all of your components are the greater the potential for accuracy.
For brass that will be lost at a match it would seem pointless and a waste but I'm sure some may still do it anyway.
 
In what rifles?

With what brass?

Russian brass in a Surgeon Scalpel? Yes. Finnish brass in an AK47? No.

Neck turning improves concentricity but induces doughnuts at the neck/shoulder junction. So neck turning leads to neck reaming... more tools.

Think hard before you jump down that rabbit hole.
 
I had to turn my Lapua necks when going to 6x47. I was having 90% crunched necks. This was useing a non bushing die I was told at some point Forster changed the ID and you can send your die out to open up for ten bucks but figured the turn necks in the long run would work out better