You bring in your artboards or images or you add shapes, and you want to evenly space them out.
Just hold down ALT and → to space them out horizontally to the right, or ALT and ↓ to space out downwards. It keeps the leftmost (or topmost, respectively) element static and moves the others evenly by adding space.
ALT ← and ALT ↑ will decrease the in-between space.
