Also can be a good way to stretch spine after sitting a great deal. Proning is also very good for stretching flexors and back. Supported standing is a good place to start some closed chain exercises to strengthen muscles in the lower extremities. Incidentally, it's also a good time to strengthen uppers. Mentally it is encouraging for patients to stand and perform activities such as reading, folding clothes, etc.
Many patients request standing in PT as the first activity in a session.