When is being able to cast Mending as an action more effective than taking a minute to cast it?

Question

In Tasha's Cauldron of Everything, there is a rare magic item called the Lyre of Building, which allows you to cast Mending as an action. Normally, it has a casting time of 1 minute, so this (if nothing else) allows you to mend things ten times as fast. However, I'm wondering if there are situations where you would want to cast Mending with your action in combat. I'd like a list of situations where Mending would be helpful in combat (For example, a list of creatures (such as an Autognome from Spelljammer: Adventures in Space)

Lyre of Building
Wondrous item, rare (requires attunement by a bard)

While holding this lyre, you can cast Mending as an action. You can also play the lyre as a reaction when an object or a structure you can see within 300 feet of you takes damage, causing it to be immune to that damage and any further damage of the same type until the start of your next turn.
In addition, you can play the lyre as an action to cast Fabricate, Move Earth, Passwall, or Summon Construct, and that spell can't be cast from it again until the next dawn.

Mending
Transmutation cantrip

Casting time: 1 minute
Components: V, S, M (Two lodestones)
Duration: Instantaneous

This spell repairs a single break or tear in an object you touch, such as a broken chain link, two halves of a broken key, a torn cloak, or a leaking wineskin. As long as the break or tear is no larger than 1 foot in any dimension, you mend it, leaving no trace of the former damage.
This spell can physically repair a magic item or construct, but the spell can't restore magic to such an object.

Answer 1

It's never more effective, but always more efficient

If you can cast mending as an action, it takes six seconds rather than 60 seconds. This is, by definition a more efficient way to do it. Also, the effect is always the same effect, so it never is more effective.

Overall, since the game does not have a lot of focus on breaking weapons, or on shredding armor in normal combat, and in combat unless you are in very unusual circumstances, you care little if a mundane object is broken or not, there is in practice very little need for this unless you play an artificer. The kinds of things I have seen mending used for (polishing up used weapons, putting back together damaged vehicles after combat) often also work when it takes a minute, as you can do it over a short or long rest.

That being said, here are some circumstances where you might want to take advantage of shorter casting time of mending:

• Healing a homunculus servant, as per @ThomasMarkovs answer in combat

• Repairing a steel defender in combat (it heals 2d6 hits, like the homunculus servant)

• Repairing a broken weapon, or key you need to lock or unlock a door to escape

• If you play an autognome from Boo's Astral Menagerie, and mending is cast on you, you can spend one of your hit dice to heal

• Shackle someone to a wall by mending a broken chain

• Repair a broken gear in a portcullis you want to lift or lower

• If something is broken multiple times, for example a shattered vase, faster mending can allow you to put it together in reasonable time frame, although that is not a combat application

Answer 2

Healing a Homunculus Servant is a bit more convenient.

The artificer infusion Homunculus Servant creates a little robot friend that can be healed via mending:

The homunculus regains 2d6 hit points if the mending spell is cast on it. If you or the homunculus dies, it vanishes, leaving its heart in its space.

While in most non-combat situations it probably wouldn’t matter, it does make healing your servant via mending in the heat of battle possible.