When you do yoga or sports, breathing in through the nose is good.
It hydrates the air and is probably more efficient.
When singing, we generally want to breathe in through the mouth.
Yes, the air will be dryer.
But doing this helps you to:
Get your mouth into an open position before you start singing
You get to lower your jaw, flatten your tongue, lift your soft palate using the hot fries
technique (this is explained in the free ebook