Why does OS X Yosemite come with the firewall automatically disabled?

[iMore Question]

Why does it come with the firewall automatically disabled?
Are there any pros/cons to having it turned on or would you recommend keeping it off?

 

[Bigeric23]

I would recommend enabling the firewall unless you have a specific reason not to.

https://support.apple.com/en-us/HT201642

 

[Just_Me_D]

A good deal of people who connect to the internet have routers/access points that have a built-in firewall unlike back in the day when you connected directly to the internet.