I've just got a quick trick for you today. Direct boxes get used improperly all the time. People use them when they need to get from a line level signal on TRS connectors to XLR connectors. While this setup will pass audio there's an impedance change going on in there that's not doing you any favors. On a side note I wish there was a test you had to pass before anyone would sell you those mic cables with XLR on one end and TRS on the other. They have a purpose and it is NOT plugging a low z mic into a line input. But I digress.
Direct boxes are useful for more than just getting unbalanced line level signals down the snake and into a mic input. One common use is to feed line level outputs to mic level inputs, like matrix outs to the mic inputs on a camera. Passive DIs are bidirectional. You can even go a step further and daisy chain multiple DIs to feed a bunch of cameras at say, a press conference. The right way to do it is with a distribution amp but in a pinch a stack of DIs will do the trick.
You can use this same trick to feed into mic pres in the studio. Take a track that you pulled in through a garden variety A/D converter and send it out for some tube warmth, even if the external channel strip doesn't have line level inputs. The DI will make sure those inputs see the right impedance and aren't loaded improperly.