I take the trains all the time in Brooklyn, and live here, but the person you're responding to isn't completely wrong; there's a fairly large patch of north Brooklyn/lower Queens that has pretty bad train coverage.

https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Of...

Also, in Brooklyn, there's a lot of places that do have train coverage in the most technical sense, but that means they have exactly one line near them. This is fine, but it can be annoying if that line is your main mode of transport and it gets shut down for whatever reason.

When I lived in Manhattan, even in the less-covered Washington Heights, it was comparatively easy to find another train nearby if the train I was planning to take was down. In Brooklyn, unless you're near the more metro-ey hubs, you might just be out of luck (or just take the bus).