It's used for Simplification of Mathematical expressions may be invovling with symbolic representations or expressions or Algebraic simplifications.
Simplification of expressions, Matrices, Logarithms or exponentials and algebraic simpler steps and Calculating the results from the expressions if values are available.
The simplification may be of type- Fraction, Numerator-Denominator form, Combining, Expanding, Factoring, Collecting, Rewriting, and partial fractions etc kind. If one wants to use particular form of simplifications then these mentioned commands can be used, refere MATLAB help -> Functions to Rearrange Expressions.
Hope this will help. Thank You.