Combine[expr] puts terms in a sum over a common
denominator and cancels factors in the result. Combine is
similar to Together, but accepts the option
Expanding and works usually better than
Together for polynomials involving rationals with sums in
the denominator.
Combine[((a - b) (c - d))/e + g]\frac{(a-b) (c-d)+e g}{e}
Here the result from Together where the numerator is
automatically expanded.
Together[((a - b) (c - d))/e + g]\frac{a c-a d-b c+b d+e g}{e}
If the option Expanding is set to True, the
result of Combine is the same as Together, but
uses a slightly different algorithm.
Combine[((a - b) (c - d))/e + g, Expanding -> True]\frac{a c-a d-b c+b d+e g}{e}