Hello,
When you want to build something, it can cost a lot of APM because you have to delete palissade, wall, farms or houses to have enough spaces for your foundation.
With an hotkey it could be great to display where you can build if you delete your own building. And also when you click (with the hotkey press) to build, it will destroy building who occupied the space of the foundation and place the foundation.
It can save you a lot of APM.