[Sandman]

Most thaumaturgy spells affect the mind. In practice, this means spells which cause damage to non-mindless units, fear-causing spells, beserk-causing spells, spells which steal enemy units, ritual spells which cause enemy units to desert and so on.

It also has teleport spells, spells which reveal magic sites, remote attack spells, spells which cause disease and anti-undead Death spells. It has a few anti-buff elemental spells as well, like dessication and bonds of fire, but these are not very effective.

Most nations will want to research to the Thaum-2 for the site-searching spells. Past that, it's generally astral, death and nature nations which benefit.