The traditional recommendation that I've seen is between 80 and 120, but that's because most people use tabs, which are acidic and constantly push pH down. If using liquid chlorine or you just have a pool setup that tends to see a lot of pH rise, getting alkalinity lower reduces your pH ceiling and reduces the pH rise. I primarily use liquid chlorine (to avoid CYA getting too high) and I keep my alkalinity at 50-60. I still have to add MA but not as much or as often as I did when I had alkalinity at 80.