Show the number off full days entered in a certian calendar somewhere
This feature could eg be helpful for people in the thourism industry, when working as a tour guide. By just entering the tource you already completed and the ones yet to come it would be easy to count the number of days you had work.
This number again can (depending on your employer) be important for your payment.
Another cenario: During corona time (thank god its over) this would have helped to count the days you have been working in home office across a whole year. There are certainly more applications for this feature.