I have an almost 3 year old Chihuahua(my avatar picture).
I had her fixed for a couple of reasons. One, because I was not going to breed her, she was too small and I was inexperienced. Two, so that we didn't have to deal with the monthlys. And three, to keep her calm.
She is the best little girl. She was crate trained and potty trained by the breeder. We only put her in the crate at night, with her potty box. She was so tiny and winters around here are very cold, having the potty box was great. We used shredded paper, the same as what the breeder did.
It wasn't until my cat passed away that we stopped putting her in the crate at night. She now sleeps with us in her own little blanket.