These are simply stationary mobs you can place in a guildhall. They are decorative guards(etc) but also serve as the perfect throw/archery/spell/song target and can be placed near a regeneration pool to make catching up on rarely used spell types/weapons a snap.
Seems to be spell casting only that you can use these to raise skills. At least I have not found a way that melee skills will increase using these. (Note: the Rangers Hail of Arrows spells WILL increase Archery skill.)