This is a great way to protect important monsters from being destroyed last minute by battle or by a card effect (depending on the Union Monster used).
One such use is equipping an "Oilman" with this cards effect to something like "Cyber Twin Dragon" in which a "Limiter Removal". This would allow you to attack twice, and draw 2 cards if you destroy 2 monsters in battle, and would protect the "Cyber Twin Dragon" from being destroyed at the End Phase.
Dark Blade and Kiryu Combo, when Kiryu equipped to Dark Blade, after Kiryu tributed for its effect, use this card to equip it to Dark Blade again to boost Dark Blade attack power.
Dark Blade, Kiryu and Double Attack Combo, If you have Dark Blade and this card in your field plus Kiryu and Double Attack in your hand, you can inflict direct damage to your opponent twice with Dark Blade. Use Double Attack, select Kiryu as a cost, and Dark Blade as the effect target. Use this card to equip Dark Blade with Kiryu, activate Kiryu second effect to allow Dark Blade attacking life point directly.