I like to send tempos to hardware and software that use tempo based effects such as delays. But I don't like using MIDI clock when its not needed (to reduce MIDI data). In my case, I have software apps that can follow Ableton Link, as well as a HX Stomp that requires a series of tap tempo commands (CC 64 to simulate a tap tempo button push). In Setlist Maker I:
1) set the tempo of each song, and set the length of each song to 10 seconds (just enough time to get everything locked to the tempo)
2) enable MIDI clock
3) Use the Custom MIDI option ...with Code field to send the HX Stomp the required tap tempo commands (in hex)
4) Enable Ableton Link (for software plugins in AUM that use tempo
5) In Layouts, send MIDI on Song Selection
When I select a song, all of the needed tempo info is sent to all my devices, and then MIDI Clock stops sending after ten seconds.
This tip is only useful if you don't use a song length time to time all of your sets and songs. And you don't want to use it for stuff that needs an ongoing tempo to lock to (such as a looper). Its very useful, though, to set a song's tempo on all your stuff.