The first one is the banns and the second one is the marriage certificate, which references the former by dates at the bottom that coincide with those on the left side of the banns. You have process records, banns, the license (in some cases), and the certificate. It could take a month or more to churn through this process for the user; however, it's a gold mine for genealogists.

Some time between 9 Feb and 19 Apr 1910 in the church. The second certificate lists when it was registered only, not the date of the wedding.

This is incorrect - you may be confusing these documents with the marriage promessa that was used in the Kingdom of Two Sicilies between 1815 and 1865, where the civil document was only a legal promise to marry but the marriage itself was still celebrated in the church. These documents refer to the civil marriage process in the Kingdom of Italy.

Between 1866 and 1929 in Italy religious and civil marriage were separate and only civil marriages were recognized for legal purposes. Most couples still had a religious marriage, many times on the same day as the civil marriage, but some couples opted only for a religious marriage even though it meant their children were legally illegitimate (they might have entered into the civil marriage years, or sometimes decades, later).

Depends what you input to your DB. I log banns' dates and marriage contracts since Gramps has an event type for both. The witnesses on the banns could be relevant later elsewhere, for example.