Subbing NIN on WAR or with weapons that cannot go below the delay of 180(i think) is also useless since you actually gain TP slower, the delay added together by both weapons are caculated as a new delay and not as seperate weapons, hence unless you can hit both under 180(where a weapon will never gain less than 5 TP and the delay of weapon dictates the ammount of TP gain), Dual Wield is actually a cripple to yourself.

That being said WAR/NIN, THF/NIN, and RNG/NIN is most commonly used, and all have their uses, however they are more for safety issues for RNG and WAR, and for THF and NIN(main) they are more for explioting the TP floor.