From my experience there were issues with indexed files stored on external media, where starting a search in DT resulted in a spinning wheel while sleeping drives were being spun. This was very annoying, especially in my case with a 4-drive RAID. I don’t know if this has been fixed since then, as I’ve removed all indexed files from my DT database and imported them properly. If you’re indexing because you’re concerned about database size getting too large, I’m happily running several databases of around 20 gigabytes and 10k items each. Others have probably pushed this much further. Selective sync to iOS makes this perfectly useable.
Just my 2c.