I inherited Weatherby .300 Magnum Mark V Deluxe and Browning BAR Grade V 7mm Rem Mag rifles from my dad. I bought Norma brass and a set of Redding Competition Neck Dies for each. After firing and neck-sizing the cases 3 or 4 times, they became difficult to chamber so I full-length resized them. When I used a micrometer to check the cases I noticed a slight bulge above the belts. Larry Willis lives near me, so I was able to get one of his dies in just a couple of days. It removed the bulges and since then I've used it every time I full-length resize.Not once have I ever found the need for this die.
If you want long brass life, size correctly in the first place and avoid rifles having chambers that DO NOT support the case head just in front of the belt. Trust me, these chambers are more common than you think.
Also, some brass is thin in front of the belt, the belt and around .040"-.060" in front are part of the solid head, in all but a few brands, there would be no expansion in that area to justify the Larry Willis die.
Anyway, if you feel the need to spend $100+ on a die you may never need, go ahead.
Maybe it's just me, but I thought it was a bargain compared to replacing my dad's rifles.