If the defendant pleads guilty he/she waives his/her right to appeal. If the case proceeds to trial and the defendant is convicted, he/she has a right to appeal any conviction. If successful, the conviction might be overturned or modified. In some cases, the case may have to be retried, resentenced, or the prosecution may be barred from retrying the case completely.  The appeal process can take anywhere from 18-24 months before a decision is made.