When does the double bowline matter? When you use 8mm as an anchor.

Expensive prep school anchor, Dead Preppies might make a good name for a band. The carabiner is an unnecessary link in the chain and the tree is too small.

Everybody should have 2 anchors? Not if one is a potential projectile.

Single bowline in 8mm, this is where not using the double bowline can make a difference.