Can I use the defroster if I have bypassed the heater core?

I have yet to see the windows frost in the 7 years I have been down here. (from Bay/Sacramento area) Thanks for the info. If I was somewhere colder, like where my folks are from in Kenosha Wisconsin, I would have replaced the heater core. Here, I am fine with the temp. LA weather forecast is a cliche for a reason I guess.