If incapacitation was not an issue, probably I was never using cross-class skills. The damage is lower (without affinity), cooldown higher...
i.e. I use leg sweep with every class because I don't have a formal substitute, or I need more stun's skills in my rotation.
If I'm tanking as marauder, I need taunt and provoke. If I'm tanking as gladiator, do I need taunt?
I can use some skill from conj if I'm thau, but does it really worth? less damage, cooldown... and both have direct spells and DOT spells.