The new Lock parameter option in Revit 2011 was nice enough, I suppose, but until recently, I did not find it improved my productivity much. I just discovered that selectively locking and unlocking parameters solves the old problem "breaking" families when setting equality constraints that include other parameters.
The attached image is not where I discovered this trick but it is a good example. To ensure pulls align correctly, the pull location is controlled with a formula. We have four (4) versions of a triple drawer cabinet with differing locations for the equality constraint. In the past, when I built these families and then used SAVEAS to create the different versions, it was tedious to continuously remove constraints, set the equality, then add the constraints again. Selectively locking and unlocking parameters in the beginning solves this issue.
Unfortunately, the batch upgrade locks everything by default. Personally, I wish the opposite were true.