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.