Upgraded to a standing desk last year. At first I didn't add my existing keyboard tray since the desk height can be adjusted for correct keyboard ergonomics. Very soon identified some problems:

1. My display cannot be adjusted high enough (this can be fixed by putting a book under the display).

2. Keyboard and mouse take up valuable space on the desk.

3. (most important) Display is physically closer and occupies more of my field-of-view. After a day of work this made me dizzy.

So now I'm happily using the keyboard tray again.