Fire Emblem: Awakening

Depending on how you measure "efficiency" you may want to level a character to level 20 in an unpromoted class (that has a promotion) before using a Master Seal on them. The cumulative level is only updated when Second Seals are used not Master Seals, and the internal level is identical whether you go to 10 or above it and then use a Master Seal.

So you'll get dinged as if you had levelled it up to 20 anyway, after you promote, so in game terms its essentially free stats. On the other hand this consumes your own personal real life time to do this.

On the other hand there's no reason at all to level classes that don't have a promotion past the last even level after their last skill though, unless its the final class or you're deliberately grinding for stats the class has high caps in.

(The cumulative level is updated by (Internal Level - 1)/2 rounded down, so using a second seal at level 15 and 16 both yeild the same 7 level adjustment).