As above.
With the electric roof there is possibility that on lowering the bellows could blow out trapping the canvas in the scissor mechanism, which could leave a hole in the fabric and a small bump in the aluminium roof.
This event can be mitigated against by ensuring a window or door is open on the lee side to allow the air being squeezed out as the bellows closes to escape out of the van. The bungee is designed to complement the closure design by pinching the sides in.
I personally, and this is me and not a general rule, advocate a mark one eyeball approach. When the roof is about 3/4 lowered just leap out and look along the length of both sides to ensure no fabric is trapped. It only takes a few seconds.