While you can use both dimensional constraints and constraint parameters in a block definition, only constraint parameters will display editable custom properties for that block reference.
Constraint parameters contain parameter information. The parameter values can be displayed or edited for the block reference. A constraint parameter can only be created in the Block Editor.
The above block definition contains both a linear constraint and a horizontal constraint parameter. The horizontal constraint parameter includes a grip, while the linear constraint does not. The horizontal constraint parameter is also dynamic, while the linear constraint is not.