When a unit's attribute matches the song attribute, the unit gains a 20% (+ additional matching bonus from the Bond Board) boost to their Stamina and Technique stats. The boost does not apply straight to their Appeal stat, instead, it applies as a bonus to the Voltage gain from taps. (This is why the attribute bonus does not apply to the Appeal part in the SP Power formula.)

(Note that the SBL 20% boost is not the same - it actually applies the boost to the Appeal stat.)

When an accessory's attribute matches a unit's attribute, that unit alone gains an extra 10% for the accessory's stats. The other units in the subunit are not affected if they have a different attribute. Additionally, there is no bonus for matching the song attribute.