Xanthan gum is used to change the viscosity of a mix or add a little "slip" to the mix. Here's some of my notes about xanthan gum.

• DO NOT use Xanthan gum with BTMS!!!!!! These ingredients HATE each other's guts! LOL!
• To hydrate xanthan gum, add it to room temperature water and wait for 15 minutes before heating.
• A better way would be to add it directly to water and use "high shear" (ie: a stick blender) to incorporate it into the mix.
  It's said to be a pseudoplastic, meaning it will thin out with high shear, but will ultimately thicken back up
• Usage rate:  0.1 - 2.0%
  (if used as lower levels, it could cause lotion to separate (WTF))

More direct notes about Xanthan gum can be found here for PAID Memberships