Changing this speed in the middle of a song can create interesting grooves, especially when using speeds like 3ppq or 6ppq which gives a triplet feel
Note that the Midronome is only applying the change on the next beat (next quarter note), so that you never end with a out of sync ANLG clock (which would start in the middle of a beat f.x.).
So when changing this setting Live, do it right between two quarter notes, then you are sure the change will be made on the next quarter note. I hope that makes sense