Spike is Twilight Sparkle's pet, and a Dragon. In my opinion, this is how Spike is.
Spike is *Cough cough* Unnecessary. Suprised? Well, he's only comedy, and doesn't do anything with the plot. The only thing where Spike actually does something important is when he saves the Crystal Empire? I think it's called that.
But, still, they could have easily made Twilight save it anyway, but they needed to get Spike some attention... Sorry for आप Spike fans. It's just true. Think about it.