There are many reasons people take part in research studies. It gives patients a chance to access medicine not available for prescription to the public. If this is the case, remember the study is being performed to discover if the drug works and to see if it is safe. This means there is information unknown about a drug therefore classifying it as experimental.
Often the process of collecting information in the study will allow your doctor to find out more about your disease and the effects it has on you. This may allow you to benefit from better treatment after you have completed a trial.
Lastly, a trial may not benefit you directly, but the information gathered may be of help to other patients with the same condition. Many patients derive satisfaction knowing they are part of the effort to potentially reduce the suffering of other people.