When I first started using Revit, I thought, "Awesome, I can lock every little thing together and it will be great!". And, it was, for a while.
We are only human, however, and eventually those constraints become a little fuzzy ("What did I lock that object to again?"). Or someone else in the office needs to work on the project. Suddenly, Revit does not want you to move anything - or that's how it seems.
There are certainly times when it is ok, even wise, to constrain certain elements. I mainly constrain elements such as walls, roofs and floors to grids, and I do not constrain much else.
Please don't tell Revit to constrain every little thing. It will be bad for you, and it is bad for Revit performance.