Rejects inputs that do not all have the same number of dimensions, which the operators that combine several inputs require: shorter shapes are not left-padded with 1s, because the first dimension is the batch dimension.
See also
Other Shape Assertions:
assert_dim_in_range(),
assert_known_dims(),
assert_ndim(),
assert_not_batch_dim(),
assert_positive_extent(),
assert_same_batch_size(),
assert_shape(),
assert_shapes()