Researchers often induce stress upon the tolerant varieties to unravel the underlying mechanisms associated with their tolerability so that it can be helpful in further incorporating the mechanisms in the sensitive ones. Any plant that is tolerant to certain stress suggest some internal antioxidant defense mechanism or any kind of stress responsive pathways that works in accordance with certain genes, transcription factors or any kind of second messengers associated downstream of the signaling pathways. So, before proceeding towards any kind of abiotic stress related researches one should thoroughly know about the mechanisms that is actually helping the tolerant varieties withstand such adverse conditions.
In addition to the view by Mehzabin Rehman, I believe that Drought tolerant varieties are more sustainable and they reduces usage of natural resources.