They are survivors from the days of really long duration cams that featured a lot of ramp time.
Ramps being a necessary evil from a cam wear perspective, so back in the day when the valve train supporting cast had a nearly impossible time getting to, let alone exceeding, half an inch of lift; these lifters allowed some lower RPM bleed that allowed the valve to stay seated as ramp was used without moving the pushrod and its top end connected parts. This came at the cost of ticking at idle and low revs and probably some loss of overall lift and duration in the .050 to .050 range as you have to pay for everything you get in one place somewhere else. So in the end you get back some of the bottom end quality perhaps at a small top end cost and some lower end noise.
Today the trend is to reduce ramp time thus total duration, pack more duration between the .050 lift measures, plus we tend to add more lift. These days .5 inch is not uncommon and competition engines are at .7 inch or more.
So today if you are looking at a modern cam and it’s valve train the Rhodes are unnecessary.
Good info. I run a .630 in my daily driver. Fun for the whole family. Technology has really come along way, but man, i would have loved to see Ed, James, VIc, Don, Miles, Carrol racing in their primes..