In Web TimeSheet version 8.10 or higher, users can enter comment for each Time Off day taken when they add Time Off's on their timesheet.

More Information:
When users don't have the access rights to add Time Off but only to book, then Web TimeSheet allows only one single comment for each Time Off booking. For example, When an employee books Time Off with start date (Monday) 1st June and end date 5th June (Friday), (considering all 5 days as working day, no Holidays in this period) then all these 5 days are seen as one Time Off booking. Hence, only a single comment is allowed.
For instance, if an employee likes to mention different reasons/comments for each Time Off day requested, then he/she will need to book multiple Time Off's. Time Off booking for each day indicates that the employee will need to raise 5 Time Off booking instead of one.