Do you mean you've only had all three characters as warriors?

If you do, then I'd say yes some of the other dress-spheres are practical to use. For example I'd certainly use a black mage and white mage at the least, because you'll need someone to cast magic (for those enemies who aren't harmed/harmed much by physical damage) and you'll also find it very useful having someone to cast stuff like Curaga and Life, not to mention other White Mage spells.

Gun Mage is another useful sphere to use as you can learn Scan and it's better than gunner.

Personally I've assigned two main dressspheres to each of my characters, and am having them learn those. Paine is Warrior/Gun Mage, Rikku is Thief/Black Mage, and Yuna is Gunner/White Mage.

The only thing I'm not really bothering with, at the moment at least, is Songstress. But you will definately need Black Mage/White Mage at some point. Thief is useful for stuff like Pilfer MP especially if using the same character as a mage as well.

Basically, all the dress spheres have different skills and abilities, warrior just has physical attack stuff, and you'll need magic as well as this, if not anything else. You will need to use different dress spheres depending on your situation. It's not practical to use warrior all the time for everybody.