Research says it helps, and subjectively my n=1 in Leadville from Sea Level says it helps.
One thing I noticed is I acclimated faster - I felt a lot better on day 1 last year (with heat acclimation) than I had the prior 2 years.
Although I was training at the same sea level FTP, my performance in Leadville, and my altitude-adjusted FTP was higher by the time I got to Leadville last year (Did some of the same intervals on the same days leading up to the race, compared power, heart rate, etc. - and there was performance difference)
Now, it could be that I was just in better overall shape, but the FTP I was training at was the same, and volume / program leading up was pretty much the same too.