Effect of xanthan gum on agar agar gels?
In lower concentrations of Agar Agar you'll have weeping (Syneresis); Xanthan gum is generally used to lower syneresis when combined with other hydrocolloids. Apart from slight texture changes; you'll benefit from less weeping.

per this paper Evaluation of Blends of Alternative Gelling Agents with Agar and Development of Xanthagar, A Gelling Mix, Suitable for Plant Tissue Culture Media; Agar Agar + Xanthan gum (i.e. Xanthagar) is considered as an economically viable alternative for using Agar Agar directly. As XG cheaper compared to Agar.