It does present a deterrent for the enemy who would like to invade and hold your territory. So it addresses that kind of attack. It does not address other kinds.

In a war, your losses don't usually concern your enemy. But they do care about how much it costs them to achieve their goals, so if you can make it prohibitively expensive, you have a sound defense.

But that's not what happened in places like Afghanistan with respect to the US. The US never wanted to "conquer" Afghanistan. If the US did want to, it could have easily killed every single person in the country and then just start building Starbucks on every corner.

The goal was to root out what they perceived as an enemy and hostile nation that harbored terrorists, and then recreate a society much more tolerant and sympathetic toward Western values. In that, there is no conquering needed. It's called nation building, and it's very different.