They can be relevant when comparing a geometry optimization with experimental data: how far the atoms "went"?
(you can use both parameters if you want to constrain the atoms movement during a geometry optimization).
But here we have two issues. The first one is related to the quality of the crystallographic data used to determine both parameters. If using powder x-ray crystallography, the data is least reliable as for single crystal x-ray diffraction.
The second one is that the obtaining of these parameters are valid only for a given, fixed crystal structure but, from the simulations you can get a phase transition where the atoms "move" more than the permitted values of U and B.