Things like Master Enslave, Undead Mastery, Gaia's Blessing and Arcane Domination can be instant battle winners in any particular situation. They are rarely used mostly because they are all Level 9. If you are on in the off chance of a game that Lasts long enough without a clear winner, or try to get one of these particular spells in order to counter another nation (Say Ermor or with Arcane Dominiation, most all other nations late in the game because of their reliance on summons) you can do it.

But they are much less of a 'go for it strategy' and much more of a 'I might as well try this because XXX made me'.

Most of the spells are uncastable by anything but a large communion or high magic pretenders/mages so I give them less thought normally until I'm presented with a situation to use them, instead of the other way around.