As a terminal multiplexer, paned
serves the same basic need as tmux or screen: it enables switching between, disconnecting from, and reconnecting to terminal sessions from one physical (well, virtual) terminal.
Where paned
differs from its progenitors is in its minimalism: there is no window management functionality beyond switching and detaching; complex layouts of multiple terminal windows is left to a real window manager.
paned
is a daemon which manages window panes, but in classic Linus Torvalds fashion its name also describes how you will feel when it doesn't work right.