I did this for about ~6 months and developed knees that ached all the time. I was running at the same time, so maybe that had something to do with it, but really I never noticed some huge health or energy shift.

The thing I will say about it though is that if you're tired, standing keeps you paying attention whereas sitting can make you slouch and relax. This is useful right after lunch, but all day? Save your legs the trouble and join a gym if it's your physical health you're worried about.