Getting all my old Juyohin together, since Dr. Kaitlyn was kind enough to pick me up a new Kifuda from Kitano Tenmangū, I am able to return the one I've had since I left Japan.
We return Juyohin at the end of every year to be ritually burned and to release the spirit of the item. It is believed that after one year the items stop being effective. This however also serves a secondary purpose, it is a way for shrines to raise funds outside of matsuri and local donations, and a way for Shinja to support their shrines.
Other etiquette regarding the return is to also include a small donation for the proper disposal of the Juyohin. The amount is up to you. I also try to make sure my ofuda are properly cushioned in the return box to prevent them from being bent.
Personally I follow the principle of: if an item you received is not something you can easily get a renewed one for, then you are fine to hold onto it until you can obtain a new one. As I am well aware that with the current state of the U.S. tariffs impacting the costs of shipping, as well as for Shinja far away from any shrine, expecting them to constantly have the funds to ship Juyohin back to the shrine they obtained it from, or be able to donate to receive a new one every year is not always doable. And I don't think the kami would mind it particularly much anyways, as sincerity is a major part of worship.
The exception to this for me personally is if a Juyohin gets significantly damaged or dirty, then it's a good idea to send it back to a shrine as it is likely reaching the end. Albeit there's also the belief if you lose an Omamori (it fell off your bag) then it did its job at protecting you, which is a nice sentiment, but I try to replace them before they get so damaged they fall off.
