Handseals

Hand Seals, otherwise known as Hand Signs, are a sequence of hand combinations, often applied by Shinobi in order to produce a range of different Ninjutsu, Genjutsu, or even rare Taijutsu. Hand Seals serve as a mean to aid in regulating one's energy, and different techniques often require a different range of seals. Appropriately, hand seals are often associated with Incantations - a means of power regulation applied by those who utilize Mana, as opposed to Chakra.

Overview
In essence, hand-signs are closely associated with the various Tenketsu located throughout the body. Given that the Tenketsu are most accessible in the hands and feet - although primarily in the hands - it is for that reason that handseals are often applied. In essence, the different combination of hand placements allows the body's tenketsu to meet, often with varying results.

With the connection of one's tenketsu, the user will then readily be able to mold their chi in a different set of ways or mannerisms. Certain seals, naturally, are more applicable for certain chakra-based phenoms - such as the Tiger seal being more prominent when using Katon Release techniques. The art of handseals are subject that still undergoes great scrutiny in investigation to this day, as the various Shinobi villages still seek for ways to improve upon their reliance of these crucial hand formations.

Nevertheless, given that hand-signs simply aids in molding one's chakra in various ways - in theory it is quite possible for someone to become proficient enough with their chakra to remove a need for hand-signs all together, no matter the skill. This factoid also is why those with high proficiency in a nature release, or in chakra control in general, often can employ a smaller amount of seals to produce the desired effects.