Effects of frequently turning on and off power in the grid
Massive changes in load may require starting up or shutting down generation equipment. Rather than start up a fossil fuel plant, it's more economical to use load levelers to improve efficiency and reduce operating cost.

Changes made by a residential load, though, are negligible. The only effect you might notice is a slight dimming of lights on turning a large appliance (or brightening of lights on the opposite side of a split-phase line). You might destroy the appliance switch or relay contact if you cause an arc, but that's considered normal wear-and-tear.