You might—I do. Your inverter won't power the house when the grid supply is down. Why? Well, because if the grid supply's down, it's probably because there's a line down somewhere. Therefore there's a lineman trying to pick that line up somewhere. He's going to be handling both ends of a broken, downed line. The generator-side line is tagged out, that's safe. The house-side line? Well, that's up to you—and so your equipment will deactivate to avoid creating a safety hazard for grid maintenance staff.