I have found it to be good practice to rename sketch variables if they are to be used in equations. This applies to variables on either side of the equation.
Sketches have a tendency to recycle parameter names. Suppose you use a sketch dimension with default name of "D1" in an equation. If you delete that dimension at a later time, SW might (it has in the past) reuse the name "D1" when you add a new dimension. That new "D1" will be used in the equation. This can be a problem, especially if the old and new dimensions do not measure the same parameters.
Another benefit is the ability to switch which dimension is being used in an equation. If you decide that a term in the equation should be measured differently, you need only change the name of the new dimension to that which was used in the equation, and rename or delete the old dimension.
