In any case, returning on the matter of handsigns, they are indeed shortcuts intended to fasten greatly a summoning process, in a matter of seconds. As explained in the lorebook, using predetermined sequences can cast powerful spells in the blink of an eye. However they will limit the spells the ninja will cast by their very definition: the number of combinations is finite, and they remain a simplification that always lead to the same result for the same combination. If the ninja is after more complicated or specific summons, they will have to go through more traditional and lengthy means, such as seen in the Kugane Castle dungeon, where shinobi slowly summoning voidsent abominations can be witnessed.
Balmung:Â Suen Shyu