While it kind of still falls under the same situational category as resistances, there is also the situation where you're trying to reduce collateral damage. While fireballs do not directly damage objects by the book, they do ignite them. Conversely, if you do want to damage non-flammable objects, Animate Objects might be a better choice. And, of course, fireballs don't distinguish between party members, enemies, and innocent bystanders.

While it kind of still falls under the same situational category as resistances, there is also the situation where you're trying to reduce collateral damage. While fireballs do not directly damage objects by the book, they do ignite them. Conversely, if you do want to damage non-flammable objects, Animate Objects might be a better choice. And, of course, fireballs don't distinguish between party members, enemies, and innocent bystanders. Lastly, it may be the more stealthy action, sending a dozen toy soldiers in to cut the throats of the sleeping guards instead of exploding the barracks.