Yes, that is basically my point. Within about 45 days (I would guess) of adding a book you're most likely to need to refer back to the original file as you attempt to enter and normalize the book's information into calibre. Or if you discover some kind of issue with the book which leads to re-adding, re-building or re-structuring the database. Beyond that there would be a substantial period where the filename is of no concern to the user at all.
The next time you might consider the filename is when your needs and expectations from the calibre Library change. Re-focusing your usage/intent will require changing your data and possibly your database. Which means you might need to go back to your source and see if any newly sought metadata is available therein (probably not - ebook standards are too minimal as yet).
With a well organized Library and applying "best practices" (whatever those are - I'm still working on trying to acquire them!) to data entry, there is little or no need for that filename beyond that period. Regular additions to your Library will mean that you're going to forget that a certain book still needs more work - but that is why certain plugins are so popular.
PS: Here's a possible "best practices" discussion thread:
How I Manage ebooks with calibre. I haven't done more than glanced at it since it is very highly detailed. I've flagged it for future reading after working out some database structure issues.