The question is kind of tricky.
A client who has no back injuries would be ‘ok’ for side bends with weights.
Side bends, however, are not the greatest exercise in the world. As Janet and Paul mentioned, the exercise isn’t very effective because you can’t spot reduce.
A better exercise would be farmers walk holding a weight (dumbbell, kettlebell) in one hand.
Clients may say ‘ how can I work my side muscles when they don’t move?”
Keep in mind that muscles cause movement and also act as stabilizers.
Hope that helps you out!