serger needle question

I have a kenmore serger that I am just learning how to use. I currently have it threaded with four threads to sew seams, do I need to remove the left needle, when I use the serger for three thread functions ie rolled hem?

No, just don't thread it. 

You don't have to remove it, but I would or you would have little needle holes in the fabric where it hits.  It really doesn't take that long to remove it.

You do want to remove it, or the looper threads wrap around the needle every time it goes down and the threads are then too loose to make a nice snug edging.