My initial question is a very simple one
What data elements are you asking about? At my library our current system Aleph records created and modified dates for many elements such as item records, bibliographic records, patron records, invoices, etc. Date of creation and date of last modification are both very important pieces of data and as far as I know we would like to retain them.
Information about the last modification/activity of (user) records can be relevant for deleting records - together with more criteria.
I agree with Carsten Schwill
I often use create/modify dates (on all sorts of records) when I’m trying to track down problems via a whopping big reporting query, particularly if I know the problem can’t possibly have occurred before or after certain dates. It reduces the amount of data to slog through considerably, and thus increases the speed of the queries both on the automated end and when human eyes have to touch it.
That said, our Voyager migrated our NOTIS information with a fresh start - anything with a create date of Voyager’s launch day basically means “who knows, but a long time ago”, and I’ve worked with that. BUT, that generally works for me because that migration was nearly two decades ago now, and the pressing problems are generally much more recent.
IMO, if FOLIO migrated data without its original create/modify dates, and just assigned a create date of the FOLIO launch day, it would be years before create/modify dates provide useful data again.
The respondents have made a good case for migrating create dates and modify dates from the source system. Since the json objects for records in FOLIO generally contain a create date and modify date, each library can make its own choice, I believe, on whether to migrate from the existing system or allow the migration process to assign the system date. As long as such a choice is possible, I think the question is moot and should be considered settled.