I scorned DT2 for its ugliness and redundancy with Finder functionality for a long time, but ended up trying and liking DT3. For very specific scenarios.
85% of my files I’d guess are just fine living in Finder. Another 5% or so are academic publications which are in the Finder and indexed in BibDesk. Next are 5% (bearing in mind these numbers are totally illustrative, not factual) of files which are my research data, all in Finder but indexed in a custom FileMaker database. The remaining 5% are legal documents covering a period of 120 years or so, and some related media coverage. These are all in DT, in a couple of different databases. For these documents, DT is wonderful - search is blazing fast, it’s easy to generate a saved search for a particular case to see how it’s been cited over the years, and to produce a corresponding file of notes etc.
In a nutshell, I think it works for this kind of situation - files where you need to capture more metadata and full-text content searching than you can do easily in the file system, but where’s there’s no fixed data structures at hand that correspond to each file.