For B2C: Extremely easy for the finder to contact the owner directly, without having to provide any personal information or downloading anything
For B2B: Emotional boosting for your brand. Imagine your customers associates your brand with the luck of finding back his/her valuable
For B2B: Versatile. From low-cost stickers for the masses to exclusive key chains for chosen customers.
For B2B: one of the first promotional items where usage is trackable, and thereby A/B Testing is possible