I can’t speak for others who like to break things down by daily deposits, but for me it’s partially psychological and partially practical. I’m self-employed, so my income is inconsistent and payday for me is sporadic. It’s just not that practical or possible for me to predict what day is going to be best for me to move money in one lump sum, and I have a much easier time budgeting from day-to-day if I pay things as I go.

I keep accounts in different places and they serve different purposes. My M1 account is for consistent deposits on long-term holds. I don’t care about instant trading because it averages out, but those averages would be a little better in the long term if the daily amount fluctuated based on daily market movements. It’s really not about timing the market at all. I’m going to contribute an average of $X whether the market is up or down, but $X+1 on a day when the market has moved down a bit and $X-1 on a day when the market has moved up a bit would tweak the results enough to matter in the long term. It’s a strategy I’ve used for as long as I’ve been investing and it’s worked for me. The volatility we’re experiencing now is really when it works best, particularly if you do it with daily deposits.

But we all have our strategies and theories about what works, and I’m a firm believer that there isn’t any one way to invest. If you do your research and you know why you make the choices you make, that’s all that matters. Your mileage may vary.