I always underestimate Bug-types, but oh man Struggle Bug allows it to breeze through hordes a lot. Mine played a role in the capture of some of my Pokemon, including the Espurr I used on my team (she's a Meowstic now).
Increasing Struggle Bug's power was essentially icing on the cake for this cute butterfly, and OMG it's so adorable in Pokemon Amie. I like to play with my River Vivillon (that's my native pattern btw, I'm from Australia) just to see his cute reactions.