I still remember one of the worst examples in the last Lord of the Rings movie, where after the victory at Minas Tirith, Aragorn leads his army to the Black Gate to go distract Sauron, so you'd think he wants to drag things out as long as possible to let Frodo's mission succeed... but then he promptly lets his entire army, including Rohan soldiers on foot because why not use your best cavalry on foot in a battle that you'd like to drag out, get surrounded by the Orcs. Why? Because it looked more dramatic that way I suppose and one isn't supposed to use common sense when watching Hollywood battles.