The left arm is the radius of the swing. Ideally, we don't want that radius to change during the swing. Thus, for some (if not most) golfers, you should try and keep the left arm fairly straight. Not hyperextended or anything like that.
If your left arm is has a lot of bend or you are collapsing at the top of your swing, then the tension you are describing might be very desirable-that's a swing change and it's supposed to be uncomfortable.
But if your arms and hands are bothering you, it's certainly possible that you are overdoing it.
I like to feel like my right arm takes up the slack (pulls the left arm taught). I feel some pressure in my left hand below my left thumb.