The problem with daily is that it doesn't happen that often unless you're looking at a narrow market. I just pulled the history for VTSAX since November 13, 2000 and there were only 10 times it dropped over 5% in one day. And those days were 9/29/08, 10/7/08, 10/9/08, 10/15/08, 10/22/08, 11/5/08, 11/12/08, 11/19/08, 11/20/08, and 12/1/08. So if you're piling up your cash and dividends (assuming adding to cash on the 1st of each month) then you would only be making purchases 4 times during the ~15 year period.