Neutron diffraction has been used to measure magnetostriction and thermal expansion in an unusual way. The three-axis spectrometers IN12 and IN3 at the ILL, Grenoble, France, were used to determine the change of lattice constants with temperature and applied magnetic field by measuring the angular shift of selected Bragg reflections. The instrumental resolution of this method is hardly comparable with x-ray diffraction or dilatometric methods. Nevertheless, using neutrons allows us to overcome certain experimental difficulties encountered when using more conventional methods; capacitance dilatometry is sensitive to parasitic forces occurring when applying a magnetic field on highly anisotropic samples. Since the penetration depth of x-rays is very small, slight movements of the sample change the scattering geometry and introduce an error, which is difficult to estimate. Here we discuss two distinct cases for which neutrons helped to explain the apparent discrepancy in previously measured magnetostriction and thermal expansion data.