WHY USE IT?
In musical setups that include Link, Link to MIDI makes a connected MIDI device behave like a Link-enabled device.
More specifically, using Link to MIDI’s Play button, you can start and stop the connected device at any time, and the device will start playing, in phase, at the next quantization tick — set by the Launch Quantization parameter on the main interface.
This is contrast to the typical MIDI Sync implementation, which requires all connected devices to start at the same time and continue playing — otherwise, if you stop, you risk losing beat phase.
NOTE: This is essentially Link to MIDI’s only function!
It may not seem like a big deal, but the freedom to turn your devices ON and OFF at any time can have a huge effect on workflow (at least it does for me).
Also, when the transports of all your devices behave in a consistent way — whether it’s Ableton Live, a Link-enabled iOS app (like FUGUE MACHINE!), or a drum machine built 30 years ago — it’s, well, pretty nice :]