Tips & Tricks: Merging
As of version 0.7.33, there are three types of manual Merge operations:
Normal Merge - Keyboard Shortcut M - Menu label: "Merge into first selected book - delete others"
This Merge will keep your first selected record, and copy additional formats and metadata from the other selected records that will fit into the first selected record, then delete the other records. It's used for cleaning up the database so you only have one record for each book. It tries to collect the metadata and formats from all the records into the first one you select.
Safe Merge - Keyboard Shortcut ALT-M - Menu label: "Merge into first selected book - keep others"
This Merge will keep your first selected record and all the others, so you don't lose anything. Like Normal Merge, it will copy additional formats and metadata from the other selected records into the first selected record, but it skips the step of deleting the otther records. Other than that, it's identical to a Normal Merge. It's used where you want to create a "best" record that has everything, but aren't sure you want to delete the others. It's also used to create a copy of a book record by selecting an empty record as the first record.
Format Merge - Keyboard Shortcut SHIFT-ALT-M - Menu label: "Merge only formats into first selected book - delete others"
Unlike the other two, this Merge doesn't touch the metadata in your first selected record. It merely moves the book formats from the other selected records into the first selected record, then deletes the other records. It's used when you have a book record with good metadata that you don't want touched, but you have some other book formats that were added as separate records.
If you select a few records, then try one of the merges, it will give you a detailed description (and warning) about the Merge operation, which is worth reading the first few times you use these. The information and warnings differ between the three types, and you can turn them off individually (although I don't recommend it.)