A replicant is a strange beast. There’s really only one file in the database, even if it has been replicated numerous times, in different groups within the database, with very little added overhead — just a few bits — for each instance. If any replicant is modified, all other instances are also modified. Unlike a file and an alias of that file (it makes a big difference which one is deleted), it makes no difference which replicant is deleted. The Name of a document that has been replicated is displayed in red italic font. Suppose a document has been replicated twice. There are now three instances of that document, all displayed in red italic font. It I delete any two instances, there is no longer a replicant and the Name reverts to regular black font.
Duplicating a file results in a new file that takes the same memory and storage space as the original. If there are two duplicates, and one of them is deleted, the Name of the remaining one reverts from bold, blue font to the normal regular font.
Example: When I start a new project in my main database, I’ll often replicate into the new project group some of the important references I intend to use for that project, so they are at my fingertips. But if I want to mark up or summarize or insert my own comments into a reference document, I’ll duplicate it into my project group, as I can “vandalize” the duplicate without altering my original reference documents, which I keep pristine and unaltered. Note: DEVONthink identifies duplicates not by Name, but by content. If I alter a duplicate’s content sufficiently, DEVONthink will no longer consider it a duplicate of the original document, and the Name will revert to regular black font.
Hope that helps.