That's another rabbit hole that depends on other decisions you've made.
If you anneal every firing, use a 1 piece sizing die, keep the difference between the fired neck diameter and sized/but/not expanded diameter below about 0.010", stay above maybe 0.012" on the neck thickness and don't turn too far into the shoulder, then no.
The thinner the neck, the easier it is to go too deep in the shoulder. If velocity spreads are the focus and the bullet bearing surface extends below the neck/shoulder radius, then uniforming the radius into the shoulder is a bigger deal for neck tension than 100% cleanup.
In the case of ELR chambers, there needs to be enough neck clearance for uniform bullet release over multiple loadings. Those chambers feature very long throats, half to a full bore diameter in length, at much tighter clearances than you can run for neck clearnace. The bullets start with bearing surface in that freebore. Focus on a clean release from the case and letting the freebore align the bullet. This isn't a workable strategy with BR because the throats are relatively short. Keeping the shoulder radius and it's impact on neck tension under control requires turning multiple times over the life of the case. Moving the bullet forward is a much lower effort strategy.
After they're manufactured, the reamer and sizing die set the fired/sized neck growth. The turned neck thickness determines where in that travel the loaded case starts. The shorter version is the neck thickness sets the neck clearance. Running neck clearances down to what someone on the internet said BR shooters use won't work with ELR rounds. I started with neck turned cases, 0.003" clearance and bullet bearing surface into the shoulder. Velocity spreads opened up on the third firing. Returning the necks with the same tool and settings highlighted the problem in the radius and restored the velocity spreads. Turning the necks down to give 0.004" gave another firing before the velocities opened up.
Not annealing every firing drops sizing die adjustment into the soup. For .002" bump, the die would need to be adjusted about 1/8 turn between the annealed and full hard condition (about 3 firings). With a minimum headspace chamber, the sizing die often needs to be shortened to reach .002" shoulder bump. With .008-.010" of neck movement per firing, the necks would split start splitting around 8 firings. Annealing isn't an accuracy or velocity spread thing for me. It's less of a headache than not doing it.
With standard bushing dies, sized case runout starts to increase around .006-.008 neck reduction. By standard, I mean RCBS, Redding or Forster. A one piece sizer from the same companies buys another few thou before the runouts open up. My take on runout is anything below .003" is a third order problem I don't need to worry about.
The final bit I try to address with neck turning is gas leakage. The gas leaking between the bullet and the neck is likely a small part of the total leakage, but improving it isn't much effort either. If you pull a bullet you've seated or look closely at the inside of the neck after expanding it with a mandrel, you'll see streaks where the bullet alternates between heavy and light contact. If you neck turn with a boring mandrel to 100% cleanup, that effect is greatly reduced. Lubrication of the bullet or necks also helps. 100% cleanup with a boring mandrel doesn't take any more time than 70% cleanup. You just need to have thought through the rest of it when buying the equipment.
If the gun is being used for ELR, I'll neck turn the cases even if the gun has a factory barrel. Especially if the bullet can't be seated out past the shoulder radius or cheap brass is being used.
