When I was a child I'd often stare into the laser scanners at store checkouts in awe. They were so cool. Full of rotating mirrors and lasers. The modern handheld ones are a little less cool.

But, re: "why lasers are useful", it's in the name. They're a way to get a spatial and phase coherent light source that's actually high power. In the old days they'd have to take a mercury arc lamp and put a pinhole in front of it. The pinhole gave it coherence but traded away all the intensity.