I never leave knots in my knitting. If you feel one coming just snip it out and re-join.
My sister in law was just telling me that her new sock yarn has a knot after every color change!!!!!! I wonder if she's maybe just exagerating. Could you picture that? Yikes.
I told her that if she really does have more than three knots she should call the manufacturer as her LYS has a very strict and prickly return policy.