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Nothing special actually, just a tradition which is centuries old in Bali.
Bali is known by its inhabitants as Island of the Gods.
Their sacred connection is also made by (offering) flowers like Frangipani, Bouganville and Hibiscus in all its forms; a leaf, flower or its oil.

Women do (or used to in the past traditionally) wear it in their hair and men in their headband or behind their ear.
If you ask such a man, his answer would simply be
“Oh, that’s because of the God. To make them feel good en to give me blooming thoughts.”
As for the pics with knives : it could very well be connected to pentjak silat ( setiah hati) as this martial art comes in many forms and ways.

Not only styles derived from animals but also in its variances of the different peoples and nations of the Indonesian Archipelago.

In Bali f.i. modern pencak practitioners often wear headbands. There are about four main systems considered purely Balinese.
The most prominent of these is Bakti Negara, which is firmly rooted in the old local Hindu philosophy of Tri Hita Karana.