In my particular case, the purpose was testing the equipment over a target that I can use to confirm it is working as expected.

But GPR in concrete can be used for all the purposes you mention. It can also be used to find voids, verify "as-built" drawings, etc. Some of our clients use it simply to avoid drilling into rebar when installing anchor bolts for shelving or whatever.

My background isn't concrete, so I don't do the more advanced things with it :)