In database settings, it says this:
" This is a large database, so let me choose when Metabase syncs and scans
By default, Metabase does a lightweight hourly sync and an intensive daily scan of field values. If you have a large database, we recommend turning this on and reviewing when and how often the field value scans happen."
My question is: how much, in number of rows, is a "large database"?
When you enable that, then you can configure the options:
There's no magic number - it depends. If you have a very well-indexed database, then you could have millions of rows, in hundreds of tables, each with tens of columns - and you might not notice any impact from the sync or scan.
If you see high load on your database during sync/scan and want to run those at different times, then that options would allow you to do that.