[Twan]

Master matrix are cool even for mages able to cast communions because you want your most powerful spells, and protecting buffs to be cast since round one, especially if the ennemy risk to cast some mass destruction battlefield spells, or a protective BE against your magic (casting master enslave before the ennemy has cast antimagic is always better).

Slave matrix can help to have a sufficient number of slaves counting in round one (mages using the spell communion slave must be before the master if he use a matrix, or they don't count for him in first round).