It's a useful took for pulling out nails, breaking open doors, tearing holes, breaking things, and just about everything else you can do with a metal stick.
It also serves as a nice weapon, the bar is heavier than a baseball bat and the prying ends can create some wounds that a knife can't.
Half-Life's most useful weapon is the crowbar.
Some dumbass broke into my house with a crowbar and tried to use it on me before I shot him.
Barney:"Oh yeah, and I think you dropped this back at Black Mesa... Good luck!"
Gordon Freeman, thinking to himself:
I'ma bust some Xen sh** up in here wif my 22... inch crowbar.