to sponge or not to sponge?

I have looked up a few recipes to use my very first starter in, and I've noticed that half call for mixing up a sponge and half don't.  I would imagine that making a sponge would make a huge difference in the taste, but some big names in the sourdough world don't use them.  Does it make that much of a difference?  Also, with a sponge, do you knead it or just "mix" it.  I've seen different wording for recipes and I'm not sure how best to prepare one since I never have used one before.  Advice? Opinions?