The purpose of fullers is threefold:
1. The make the blade lighter. The energy is proportionate to the mass of the blade times square of velocity with which it is wielded ( just like any other energy, including the famous Einsteinian equation
). Thus, a small sacrifice in the mass of the blade allows the swordsman to move it faster, thus increasing the energy of the cut. An example: decrease the mass from 2 to 1, and increase the speed from 2 to 4 (same proportion): the energy of the blow increases twofold.
2. Creation of fullers increases the surface length of the tranverse section. This increases it's rigidity (less bendable) The fuller creates a section of a semi-pipe, and we all know that it is much easier to bend a solid piece of metal than a pipe of the same diameter. this is why several narrow fullers are mechanically better than a single wide one. The same principle applies to the "T-spine".
3. To serve as "blood grooves", but only in horror movies
