I wouldn't underestimate the propensity of humans of all sorts to act against their own interests in service of laziness.
State-sponsored agents are less likely to be lazy and more likely to follow SOPs, but the average person (law abiding or not) is likely to be lazy/sloppy a lot.
There are stupid terrorists. However, one could argue the value to national security is negative, because of drag on the economy, resentment, and because these resources could be better spent elsewhere. Like training our own real life spies.
Unless a terrorist or spy is exceptionally stupid, they're not going to be carrying anything of value on their phone through a border checkpoint.