If it is raining enough to make eating in the Sukkah unpleasant (enough to ruin the soup or so), then one is exempt from eating in the Sukkah.
Let's say that someone was on their way out to the Sukkah to eat, when it suddenly started raining. Is there any value to postponing their meal until it stops raining in order to be able to eat in the Sukkah, or once it is raining is it just as good to eat inside?
What if someone was not planning on eating, but then it started raining and they "took the opportunity" to not have to go out to the Sukkah to eat?