True. But it would take ALOT of cash. Maybe more cash than I have on hand at the time and I like the optionality cash has given me. It is a good reminder though.

It would hardly take much cash at all. Let's say it's a 425 strike call that expired in the money at a close of 428.36. So, come Monday morning after being assigned, the option holder sends you $42,500 (per option), and you then proceed to buy 100 shares for $42,836 and deliver them to the option holder. Total additional cash expended is $336.

Even if they were deeper in the money calls, the cash expended isn't ridiculously high. Let's say they were 400 strike calls. So close on Friday was 428.36, you get $40,000 from the exercise, you spend $42,836 on the shares. Cash expended is $2,836.

Now compare this to the alternative. You have long-term shares in your account with $100 basis. If you deliver those, you will have an immediate capital gain of $32,500 (for the sale at 425). The capital gains taxes on that (at 23.8% for most of us) will be $7,735. That's A LOT MORE cash expended than the previous technique described above.