Assigning (your own) unique id to records on Google Sheets serves two purposes.
The first is that records with an ID on Google Sheets become idempotent. This means that even if someone records an entry from a sheet with that unique id twice, it will not be recorded again on that book.
It prevents creating duplicate transactions on a book.
From the point of view of a book such a unique id from a sheet is a remoteId and is accessible via the REST API or the BkperApp (Google Apps Script). This makes tasks along a financial workflow easy to automate.
Freeze the first row of your Sheet
Freeze the first row with the column Headers and besides the system properties insert an ID Column.
After freezing the first row go to the Bkper Extension and select the Generate Transaction IDs option.
The Unique IDs are inserted in each row that has data on it.