Use the tripod for all portrait shots....even with your VR lens. I'd probably use the 50 more. You can move yourself or subject in most cases to get the framing you want.
Here I am, telling you, a multi ribbon winner, what to do. ha ha ha
I never use a tripod for portraits. I want to be able to move around and interact with my subjects and not be tied down to one spot. I always use the longest lens I have available. I normally shoot with my 70-200 or 85MM.
I would use the fastest lens i have to make my camera faster and give little DOF. I don't use tripod because i shot different angles, between 3 to 5 shot per start and changing little angles from my start point.
If I shoot a model, or whomever, while I shoot, I talk to him or her to change face impressions. Sometimes you can't just shoot those with tripod, freehand is much better and comfortable for both myself to my model.
Now, using fastest lens is not a rule. I sometimes do need to zoom in and out to get perfect crop for my model. If lights are enough, I would go with zoom lens, but I might use both in one session.
but what do I know (I only had two studios myself, and working as a full-time photographer right now)
portraits, i shoot handheld. But outdoor on uneven terrain, i find a tripod to be more stable and versatile than my lightstand if im using off-shoe flash, so i bring it with me.
I take my tripod and set it up and use it for a few shots. Then I feel tied down to it and take the camera off the tripod. Sometimes I think it is a good idea to shoot on one other times I want the freedom to move around.
