Build a Stable Base
Scaffold frames are designed for use with either casters or base plates. If you skip them, the frame tubes can get damaged and structurally weakened. Set a 2x10 block of wood under each leg, even when using a base plate. This will help prevent sinking into soft soils or hot asphalt.
Setting the scaffold on blocks when working on concrete isn't necessary, but it's still a good idea. An uneven floor or a slightly cupped base plate could result in a small mating surface. The slight flex in wood ensures a nice, even distribution of weight. When you're working on an uneven surface, level and plumb the scaffold with an adjustable base jack. Never set the scaffold on masonry or stacks of wood.