It is not expected to make reliable predictions for out-of-sample data. The sampling range determines essentially the applicability of the PES range, which should cover sufficiently large regions. As mentioned above, generating configurations on a random or regular grid becomes unfeasible for larger systems. Still, the grid approach can be employed for sampling with some degrees of freedom fixed. For instance, regular grids can be used to sample configurations along the two reactive bond lengths, rXH and rHY, in the hydrogen abstraction reaction X + HY → X…H…Y → HX + Y, with other coordinates fixed.