May seem unnecessary until the day it bluntly saves the day

Ideally, 7 euros for a piece of plastic, you can find it expensive, but if you have the misfortune of losing the original cap with a goal, and that this "piece of plastic" resets the goal in the bag without making it gather dust or risk of scratching his rear lens, then 7 euros, this is nothing compared to the price of a lens, which itself does not cost 7 euros.