Standing and sitting are two totally different activities for the body. There are plenty of reasons to choose standing over sitting for activities that require attention, and sitting over standing for activities that require a calm mind.
Standing engages muscles, while sitting lets them atrophy. Standing promotes good posture, while sitting allows for slouching. The studies are plenty in regards to the physical benefits of standing, but there are plenty of mental reasons to stand instead of sit.
Standing invokes an energy to "go," whereas sitting has a stagnant energy. Many people feel motivated while standing, and sitting promotes relaxation.
Sitting and standing each have a place in any given day. For example, you don't make it to the gym by sitting on the couch, and you might find it hard to sleep standing up. Something that most people don't realize, is this also pertains to the work place.
Using a standing desk can help to solve this problem. If an employee was to stand during part of the hours while at work, not only would it help with posture and performance, but it would also help with motivation and staying awake.
If someone who is encouraged to stand complains of foot problems, or pain during standing, then there are other options to help with that. Using a high stool to alternate between standing and leaning can ease the pressure off of achy knees and feet. Also adding a thick pad under the feet can help with the pain that is sometimes experienced in the bottoms of the feet.
Trying to relax after a stressful day at the office is hard to do if you spent the whole day sitting. Your body needs exercise after remaining sedentary for many hours, and your mind craves rest after many hours of work. Choosing to stand instead of sit while doing desk work can help you to use sitting as a relaxing activity, as it is meant to be.