Suppose you need to use an aerial lift outdoors so you can work in an elevated outdoor junction box, but there are power lines in that area. Regardless of the type of lift (e.g., scissor lift, bucket truck), misjudging the clearances could prove lethal.
Always allow for movement when measuring overhead and lateral clearances. That includes “overshoot” by the operator and the need to maneuver the lift around the work area. A major factor to consider for clearances is what the wind might do once you’re at elevation. It’s not just the swaying of the platform and the cables to account for, but also the danger of a tip-over.
When measuring vertical clearances, remember the ground is probably not level. For your bottom level reference, use the highest point rather than an average.
When measuring lateral clearances, consider where your outriggers will go and where someone will have to stand when setting them up.