I ran across a thread about statistics being up to date and part of it was about stats generated by DTA (see the comment by Aaron Bertrand). Easy to identify:

select db_name() as dbname, name from sys.stats where name like ‘_dta_stat%’

Are they being used? Drop them? Assuming autostats is on, the only risk would be if DTA created multi column stats without the supporting index. Interestingly the only two cases I found were both third party apps. I don’t know if they shipped with them or if it was subsequent tuning/experimentation.

Added to my list of things to check.