I figured I never had to shoot weak hand again after our black badge IPSC course, so never practiced it much. Then on one particular match about 8 months after the course, we had two entire stages that had to be shot weak handed. A bunch of us just looked at each other, rolling our eyes, during the walk-through. I swear, half my squad scored zero on that stage. Many of the targets were 3/4 covered with no-shoots at 20 yards. They ran out of white patches and an RO had to go back to the club house to get more
Now I practice weak hand shooting at least a little bit on every range trip, and that includes twisting around barricades or barrels to throw off your shooting index. I also dry practice transfers and weak hand shooting a few times a week. That includes reloads with mags positioned on the table too, inserting them with my strong hand. There was one stage earlier this year where we could place the mags on barrels anyway we liked, but the stipulations were that we shot everything weak handed and no mags in our mag pouches.