Mostly I use one per song.
However, in some instances I need more than one.
For example:Suspicious minds needs 2 because of the Tempo change.
Shine on your crazy diamond by Pink Floyd needs 3 Registrations ....
Eric
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Genos, PSR-S970, TC Helicon VoiceLive3, Mackie 802-VLZ3 Mixer, 2 Bose L1 Pro16, Electro-Voice ZXA1 Subwoofer