In Chrome (and, I think, Firefox), dragging a tab from the tabbar to the window area causes the browser to move that tab to a new window, which can then be resized independently. This is particularly handy for reading pages whose margins follow the window width and need to be narrowed to be read comfortably (at 10-12 words per line) without reducing the width available to other tabs (whose display might be less than optimal at a good reading width). This is a relatively minor convenience function, but a genuine one, at least for me.
A very late follow up. Tear-off tab feature are landed in 0.15.0. The latest release is 0.15.310. You can update your Brave version (or you already did it ;)).