What's The Big Deal With Density? (Edited)
New buzzword just dropped.
Note: As of recent I realized that I don’t feel very strongly towards these ideas anymore. They most likely do not represent my current positions. Nonetheless, I still believe it should stay and that readers can take whatever they want from it so long as they do it with a grain of salt.
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The better you are at tech, the more difficult it is to find unique and interesting material. This sounds paradoxical considering tech is all about the exploration and application of material with learning new tricks and links being just an inherent aspect, but what happens is that with every incremental increase in your skill, the standard for each link and combo increases just as much if not more. It becomes increasingly difficult to find and create new material that is capable of meeting that standard and tricks quickly become obsolete (a.k.a. filler) as there's no way to integrate them without drastically reducing the overall quality of the combo. An example would be the ring around, which is infamously difficult for beginners and intermediate spinners alike but becomes wholly inapplicable for higher levels of tech for being mechanically too simple and having variations too limited.
This leaves you with two options:
Find new tricks which have mechanics difficult enough to meet the standard.
Create new linkages.
The first option is wholly unsustainable. Even at his peak creativity, fel2fram discovered about a dozen tricks with unique mechanics at most, and his crowning achievement lies not in the tricks themselves but rather how he applied them in linkages and combos. This is not to say that it's too difficult to find new tricks, but rather it's nearly impossible to find tricks that have wide application and are coherent with people's vision. Ankle spin is certainly a unique trick that would add originality points to any combo, but its applications are extremely limited and it doesn't fit in with the repertoire of most spinners who don't want to show their feet. The latter also applies to trick branches such as stalls and to a lesser extent fingercrosses, which is a big part of why they're not very popular.
Thus, this leaves us with the second option. Even simple combinations of the most fundamental tricks can create a lot of material.
For example, take these two links:
Charge 12 -> Bak 12
Bak 12 -> Charge 12
These links contain the same tricks, but they are mechanically unique from each other, as subtle as they may be. In both cases, it's not as simple as doing trick A then trick B. The transition in between the two tricks is itself a mechanic that makes these links unique from each other. Basic linking of unhybridized tricks can only get you so far in that it's limited in both the number and difficulty of its mechanics, thus progressing further requires the usage of hybrids. What truly separates a trick from a hybrid is not a question I have the answer to but for simplicity's sake, I'll characterize hybrids as sequences of combined tricks that together create a mechanic that is unique from the tricks themselves. More mechanics can be derived from hybrids than tricks, but more variation can be created from a single trick than a single hybrid.
Hybrids are great in that they turn combos into a sequence of dependent variables where the execution of the very first trick directly affects that of the very last trick. Where the difficulty of basic linking can be formularized to [(diff. of trick A) + (diff. of trick B)] * 1.2, the difficulty of hybrids is more so akin to [(diff. of trick A) + (diff. of trick b)]^2. Basic linking increases linearly in difficulty as execution can be chunked:
(Mechanic A + Mechanic B) -> (Mechanic B + Mechanic C) -> (Mechanic C + Mechanic D)
This is a problem considering there are only so many difficult tricks and only so much time. Such is not the case in hybrids as mechanics are so reliant on each other regardless of their position. Although hybrids are the premier way of creating difficult material and are vast in quantity, it's nonetheless difficult to find quality material as it requires you to sieve through a lot of subpar hybrids to find those of the right standard, a task that only becomes more difficult the higher the standard.
To oversimplify things, continuous tech progression essentially boils down to maximizing density (average concentration of hybrids) in order to maximize difficulty at any given level. Although it's very possible to create new and difficult combos without density, it is impossible to continuously improve while avoiding it as 1: you'll run out of tricks and 2: basic linking is limited in mechanics. The heart and soul of tech's difficulty lies in the uniqueness of mechanics, and one's skill in tech is one's capability to learn new mechanics.
Footnotes:
This essay was written with an assumption in mind. It is possible to improve in tech while ignoring density as a whole through sheer brute. You could always increase the overall difficulty of your combo by adding an extra 0.5+ spin or by extending the length of your combo beyond standard means, but improving is such a fashion is so bland and uninteresting that I consider it an intellectual dead-end, and thus I didn't consider it during the writing of this essay.