By definition, this is money that you aren't using for frequent transactions. (savingsaccounts.com)
Your point about frequent assignments & frequent transaction costs has merit, but these defects belong mostly to this strategy. (canadiancapitalist.com)
For one thing, frequent transactions mean market swings could have a bigger impact on you — if you're forced to sell shares whenever you need cash, even if the value of your investments has dropped. (investor.vanguard.com)