Yes, it is definitely an understatement: it means “I would REALLY like to do that, but I won’t/I can’t/I have a good reason not to”. Some examples I can think of: “Peux-tu venir chez moi demain soir ? -désolé, ce ...

Je suppose qu’il s’agit de la suite de notre discussion dans ta précédente question. Tu as bien fait de poster une autre question, c’est plus pratique pour étendre la réponse qu’en commentaire ! Pour moi, il s’agit bien d’une litote. ...

“ça lui fera du bien” is just an objective way to speak. That will be good for him. “ça ne lui fera pas de mal” has two meanings: Nothing to worry about. He can try it and that can eventually ...

This is a litotes, which generally tones down the general meaning of the sentence. However, in this context (because of the “enfin” that means here “not too soon”, and the exclamation point) it is probably ironic, so the effect is ...