There wouldn't if the computer algebra step was integrated in the typesetting. Rather you first derive/verify the equations in a CAS and then write them in TeX

There wouldn't if the computer algebra step was integrated in the typesetting. Rather you first derive/verify the equations in a CAS and then write them in TeX for the paper. Even if export (like Mathematica) you may still decide to fix formatting a bit doing a seemingly obvious change which ends up changing the expression.