There are several possible potential benefits to chiral switching or chiral specific drugs. These include:
#An improved (less complex, more selective) pharmacodynamic profile
#A higher therapeutic index (improved safety margin)
#Less complex pharmacokinetic profile, less complex drug interactions
#Less complex relationship between plasma concentration and effect   
#More rational therapeutic drug monitoring
#Expose the patient to less body load and thus reduce metabolic/renal/hepatic drug load
The chiral switching approach has sometimes resulted in failures and disappointments.