It's not as easy as it sounds to stay consistent with it over time (years, decades). I did all the research, read a bunch of books, and used up a lot of my time when I was looking into investing. I picked an asset allocation strategy, and planned to contribute regularly and rebalance annually.
That just didn't happen. Rebalancing annually didn't. Contributing in a timely fashion didn't. My income goes up and down, I have to pay quarterly estimates, so I do keep some degree of excess cash. invariably, I forget to invest the difference for long periods of time.
In the end I hired a financial person to just handle it and manage my money. Yes, there is a drag on returns because of it. But the alternative was being out of the market for periods of time, or off balance. Anyway, just another opinion.