driven dimension?

Sometimes get a message: Adding this dimension will over-constrain the sketch. Choose ok to create a Driven Dimension. Not sure of the meaning of this, or how and when it's created and when I might need to use this.

Julie Kumar17 days ago

Over-constraining the sketch means that the dimension is not strictly necessary. For example, if you created a square (set constraints that all four sides must be equal length), and set a dimension for one side to be 2" long, then if you tried to create a dimension for another side you'd create a Driven Dimension. This dimension is driven by the first one you created--the 2" length. They cannot logically be different from one another, because you already have in place a constraint that each side must be equal. If you're over-constraining the sketch, consider deleting all your dimensions and constraints and starting over. Think about how each one relates to the next, and make sure you're not trying to set impossible parameters.