Predictive mode can automatically display a reminder of the syntax of the LaTeX command you are currently typing in the echo area. This is enabled when predictive-latex-display-help is non-nil (the default), disabled otherwise1.
[1] The only way to add new help text definitions is to dump the relevant LaTeX dictionary to file (see Loading and Saving Dictionaries), edit it manually, and recreate the dictionary (see Creating Dictionaries).