Okay, so I have a 3 month old morkie (maltese/yorkie)... But I do not want to leave him in his cage alone when I go out... is it okay to? Will he be okay?

Have you been using it all along? If so it isn't mean to leave him in the kennel while you go out. My 4 mo old brittany is used to it and is fine. She welcomes it as her safe place. It also depends of he is still a chewer and ho well he can hold his bladder. My pup is still a mischief maker . So it is more for her safety .
Good luck

Demonbrat, the safest place for a new puppy in your home when you need to run errands, is their crate. The last thing you want to do is to leave him uncrated/unattended and take a chance he might eat or chew on something that could harm him. So, yes, it is not only okay for you to leave him in his crate when you go out, but highly adviseable to do so. We all need to run errands and what you are proposing is the normal thing to do. At this age, please do not leave your pup alone for more than 4 or 5 hours without a potty break. It is also important that your pup have as much social interaction & exercise as possible. Dogs are pack animals and require a high amount of socialization. Being left alone for too long will create a mentally unbalanced dog.

Activity stimulates elimination. Being in a crate reduces activity, making it easier for the puppy to hold it.

I think that what we call this thing affects our attitude toward it. And our attitude is going to affect what we communicate to our dog.

If we call it a "cage", it has a negative connotation. This negativity is going to get communicated to our dog- because dogs can pick up very subtle clues based on body language and facial changes that we aren't even aware of.

If we call it a "crate" or a "kennel", these are much more neutral descriptions. So maybe we should try using these one of these names.