Why does the equipment have to be dry when doing the Resolution of Phenylsuccinc Acid experiment

I wasn't sure if it was b/c you do not want too much moisture in the solid formed. Or is there a chemical reason behind it.

With any experiment involving a chemical reaction you should make sure that your equipment is dry because water has chemicals in it that may alter the result of your experiment unless it is distilled, but you should still dry it anyway.