That is always confusing to me. If I am on a bus stop: "This bus" doesn't make sense, it doesn't exist yet. Next bus, is the next occurance of event "Bus".
If it's Wednesday, the "this Friday" doesn't really make sense. There doesn't exist a Friday in Wednesday, that you call this. Next Friday however is quite clear - it's next occurrence of event "Friday" on the timeline, so it's the one in two days.
E. G. For storage and performs reasons. 5 bytes vs 9 bytes. Multiplying by amount of users and various indexes - can produce very noticeably difference. More records per page.