YES, Please do. If you’re rear-ended while waiting, and your tires and vehicle are straight, then your vehicle will be pushed straight ahead (not the end of the world). If your vehicle and/or tires are turned, you may be pushed into oncoming traffic in the case of a rear-end collision, and may be then T-boned.
There are some exceptions, like this intersection on Cambie St. in Vancouver. Here, you kind of have to angle your vehicle as per the little white guidelines:
Often, if your vehicle is completely straight like it should be, it means you can’t properly see oncoming traffic. In this case, simply wait until the signal goes yellow or red – whenever it is safe, turn. If you don’t know, or aren’t sure, or can’t see if it’s safe, then wait.
See this post for detailed information on turning left at lights: How to turn left at traffic lights.