Fibres can roughly be divided in soluble and insoluble fibres; although it is much more complex than that. Soluble fibres, as the name suggests, dissolves in water creating a fluids that could be transparent of opaque, but without lumps. Insoluble fibres do not dissolve in water, but do bind water and provide within that texture.
Soluble fibres come in various shapes and sizes or lengths. With that soluble fibres can create low to high viscosity fluids and gels. As fibres are basically combining similar molecules and with that creating polymers, think of cellulose or hemicellulose. On average looking at soluble fibres you could consider smaller chain lengths of the polymer that they resemble more to regular carbohydrates such as starch and sugar and might even behave as such, creating openings for sugar replacement. As pectins, a common hydrocolloid, is also a soluble fibre you can also imagine that with the right conditions set in either your bakery product or filling, certain fibres with a longer polymeric chain and the tendency to gel and/ or have high water binding capacity could help you clean up the label.
Insoluble fibres attract water and have a higher water binding capacity than most soluble fibers. The density of insoluble fibres are quite low and resulting in a quite high volume or bulking effect, almost looking like cotton. Once the length of fibres is being reduced the density increases. The benefit as well is that the hydration of the fibres is more instantly compared to longer fibre lengths. As the insoluble fibres bind 300-2000% of their weight in water, it might become quite inconvenient once you thought you hydrated enough and then discovering in a later moment your dough or product changes to much over time due an even higher water binding capacity.