Because "winners rotate," taking some of the cash off the overachiever's table, to fund the underachiever (which could be next years' winner), is often a wise move. ...Rebalancing has, (at least for me), worked out very well.
That said, I guess it depends on the size of your portfolio? If it's not too large, "throwing cash at the wall," might be a decent enough plan for awhile. There have been so many posts here showing that asset allocation doesn't matter too much in the grand scheme of things--at least not as much as savings rate and buying low-cost ETFs.
People can't help overthinking their portfolios. I think it happens out of boredom. When my own brain decides to turn into a financial tinkering dilettante, I give myself a few facepunches, have a cold shower, and go for a walk.
