Specifically, in 16 studies involving 70,664 participants, those w/pre-hypertension (systolic blood pressure 120-139mm Hg and/or diastolic blood pressure 80-89mm Hg) randomized to treatment had a statistically significant 22% reduction in stroke risk compared to those randomized to placebo. In fact, only 169 patients had to be treated for 4+ years in order to prevent 1 stroke (which compares favorably to the 118 w/hypertension who need to be treated in order to prevent 1 stroke).
As with any other therapy, there was a downside to these double-edged medications. High potassium, kidney failure, excessively low blood pressure, and water retention were all identified as complications & side effects of the medications. When you consider that over 53 million adults in America alone have pre-hypertension, even the small risk of side effect implies affecting a not inconsequential number of patients.
I don't know about you, but aside from kidney failure, I'd rather deal w/hyperkalemia, hypotension, and edema than the residual effects of a stroke.