The short answer is no. Usually you will not need to enter a custom date to see your current timetable.
For your 'Current Term' timetable, today's date is used automatically to generate your timetable. Therefore you can ignore the 'Custom Date' feature.
For your 'Next Term' timetable, (once it has been released to the public by the department timetabler) the date used to generate your timetable is based on a date usually within the first week or two of the next term.
To view how a timetable would appear on a specific date you can enter a custom date. Some courses may not start until late in the term and therefore they will not appear on the standard timetable at the start of the term. If you were to enter a custom date which matches the start date of that special course then the course will appear on the timetable.