An emulsifier will allow the product to wash off with water. Not sure why you'd want that in a body butter -- is it billed as a product to use for massage, perhaps? Massage therapists want products that will wash out of their sheets and towels, so an emulsified product is something they would like.
TVivian has a point as well -- the e-wax may serve as a non-greasy thickener.
There's a lot of debate over the use of preservatives in anhydrous formulations. Some argue the preservative isn't necessary. Others argue that if the product can be contaminated by wet or dirty hands, it needs one. I agree with hmlove -- it's smart to include a preservative. So if you use one, which kind -- oil soluble or water soluble? Some say oil soluble because the product is all fats and the preservative will then just mix into the product, no problem. Others say water soluble because microbial growth starts where there is water contamination, so you want the preservative to dissolve into any water and provide protection. In which case, yes, the emulsifier will help distribute the preservative throughout the product.
