Does Fusing items to shields change anything?

Question

Not including items with obvious effects, like bomb flowers, zonai devices, etc. Does fusing something to a shields increase anything? I'd assume more durable sure, but shields have a stat number of sorts... so does fusing something like a weapon or something with high fuse attack power effectively turn the shield into a second weapon or just "waste" the fuse?

Answer 1

It's uncertain if fusion on shields actually improve durability (some items may even reduce it), but these are items that you can fuse on your shields which yield secondary effects:

• Weapon + Shield:
  You can attach any weapon, horn or other melee-attacking item to your shield and use it for off-hand attacks. Simply stick your item of choice on there and use the parry function to deal out damage with your shield.

• Shield + Shield:
  There are no special effects here, your shield will simply become twice as durable. This is a great way to spruce up some of the weaker shields as you get further in the game

• Mirror Shield:
  You can use it on enemies when it's sunny by shining the light on them to stun them and force them to drop their weapons

• Puffshroom or Muddle Bud Shield:
  Puffshrooms are pretty common in the early game, and putting one on your shield has a unique effect. Once an enemy hits your shield the shroom explodes in a cloud of smoke blinding enemies. Muddle Buds are essentially upgraded Puffshrooms.

• Spiked Iron Ball Shield:
  These giant Spiked Iron Balls will deal huge amounts of damage to enemies struck with them.

• Bomb Barrel Shield:
  The deadly fusion of shield and bomb barrel explodes when struck by an enemy, and it doesn't do any damage to Link in the process.

• Gemstone Shield:
  When an enemy hits your shield, an area of effect blast will radiate out and deal the damage of whatever gemstone you have equipped, turning your defense into a pretty good offense. Depending on what you equip, it will deal different effects:

  • a ruby will deal fire damage
  • an opal will deal water damage
  • a sapphire will deal ice damage
  • a topaz will deal lightning damage

• Boulder Shield:
  If you infuse a Boulder to a shield and use parry on a breakable object, it will work the same as if you use a heavy weapon infused with material intended to break breakable objects without sacrificing your weapon durability. Only a tic goes off your shield durability.

I'm not including the obvious effects gained by Fans, Springs, Rockets, Carts, Brightcap mushrooms or even the funny (and useless?) ones like Courser Bee Honey.

Sources: 1, 2, 3.

Answer 2

Combining it with a minecart turns your shield into a skateboard

It's not a second weapon but a really funny way to travel around Hyrule and I think it is a not so obvious effect which improves the gameplay alot (at least for me).

Polygon article - Shield Surf Skateboard

Instructions

1. Fuse your current shield with a minecart
2. Hold ZL to wield your shield, jump with X and then hit A while Link is still in the air
3. Shred all pipes in Hyrule