Should End Date be exactly 1 day after start date/is end date required when all day

[ScottBTR]

eventValues.Put(CalendarContract.Events.InterfaceConsts.Dtend, newEvent.EndDate.HasValue ? newEvent.EndDate.Value.ToUnixTimeMilliseconds().ToString() : newEvent.StartDate.AddDays(1).ToString());

It looks pretty arbitrary that we're adding a day if the end date hasn't been provided. Couple of questions:

Should we be even providing an end date if it's not provided?
Why are we adding exactly 1 day?
If we need to provide a value and it will be an arbitrary number, I feel that we might want to leave a comment why about it.