It's more complicated than that. Many people call the entire "spin rocker" a "sweet spot". Saying that you should try to spin on the part of the blade
somewhere on that definition of sweet spot.
But for a triple rocker blade, you
can't spin on the front spin rocker section - i.e., by that definition, the entire "front sweet spot".
AFAICT, for all intents and purposes, except possibly when jumping, the front spin rocker section doesn't exist. And even for jumping, it's usefulness is unclear - perhaps it would be easier to vault over the toe pick if the front spin rocker section was a straight line, more like pole vaulting?
Bill_S said that he took measurements and found that side honing (e.g., parabolic blades) doesn't exist at the level that touches the ice. That it's main effect might be to remove a few grams of weight. I think he more or less seemed to feel that it was merely a marketing ploy a blade company could use to justify the high costs of their blades, but was pointless.
I'm wondering if this is like that. That the presence of the 3rd rocker segment has virtually no effect on skating, once you have removed some metal by sharpening (or by skating a lot). But it helps "justify" the high cost of those blades.
And by the way there are other terminology problems in figure skating. E.g., to many people "rocker" refers not to the curvature radius, but to the single point along the length I call the "sweet spot". Quite a lot of skaters and coaches use that terminology. And you see it a lot on Youtube, and in other videos, that teach figure skating elements.
And others use "rocker" to mean "rocker profile" - the whole shape of the bottom of the blade.
I was really hoping to get some comments on the issue I am talking about - why that spot - which you might prefer me to refer to as "the point along the length of the blade where the rocker profile curvature changes" (so many words!
) - exists, and whether it makes any sense, or is just a marketing ploy.
I admit a lot of people do buy triple rocker blades. But a lot of people buy blades with various forms of side honing too. (And people have told me they feel parabolic blades are much better for landing jumps, in spite of what Bill_s said.) What people buy doesn't always mean they have tested every aspect of what they buy.