Force develops against resistance. Growth demands constraints. When constraints work systematically and methodically, they create a challenge and stimulate the ability of overcoming it. Contemplative practices aim at achieving a state of freedom, but they pursue this goal by setting a structure of limitations around the practitioner, which works as a scaffold for their progress. In the traditional Buddhist context, this is often expressed by the mutual interplay of 'Dhamma' (teaching) and 'Vinaya' (Discipline).
There are various kinds of scaffolds. Some of them are people: teachers, communities, friends. Some scaffolds are corpora of texts, traditions, ancient lore. In some cases, the scaffold is the body itself, understood as the basis and carrier of experience, and hence also as the domain within which practice must unfold. In fact, most contemplative practices have a somatic or embodied dimension. Regulating the breath, maintaining a certain posture, listening to feelings and perceptions, playing with visualizations, are all ways of using embodied aspects of experience in order to create constraints within which one's understanding and interpretation have to move and find their own pace.
Scaffolds have the advantage of making (some aspect of) practice more visible, or rather publicly observable. It is very difficult for anybody else but the meditator themselves to directly observe a state of composure or feel a particular emotion. But counting the breath, keeping a certain bodily position, or even decoding a specific emotion is something that is much less hidden, and more easily accessible to the sight (and judgment) of others. The scaffolds and embodied components of practice are, in this sense, more tangible, somehow more concrete, perhaps even 'objective', in a way that the more intimate and 'private' dimensions of practice will never be.
This is also the major risk that comes with the (inevitable!) use of scaffolds. Looking for something to grasp, something to hold on to, something visible enough to share, and perhaps to ask recognition for, one might start regarding the scaffold itself as if it was (somehow, and magically) the essence of what practice is about. There might be some relief, on the moment, in turning a scaffold into the goal itself, since the scaffold is here, present, 'ready-at-hand', everybody can see it, it can elicit feedback, or even admiration. But they are not what practice is really about, and thinking otherwise is the 'wrong grasp of rituals and morals' (silabbata-paramasa), which is no longer a scaffold, but an actual fetter, a yoke, a self-inflicted limitation.
Scaffolds are often used to build something (a monument, a community, a party, a sect), and the idea of being busy with 'building' can be enticing and meaningful. However, contemplative practices are rarely about 'building' (even less about 'body building') and the scaffold they use are often aimed at facilitating a process of deconstruction. Scaffolds are built around pre-existing structures (often based on problematic, if not unwholesome foundations), and they are used to progressively demolish them in a methodical way, which prevents sudden and risky collapses, but also the possibility of leaving anything accidentally out of the process. Contemplative scaffolds have performed their function when nothing else remains within them. Then, they can also be dissembled.