It depends on how adept you are at creating cards, I think. If you have a non-manual pipeline that automates most of the work, I think the lifetime cost of reviewing a card a few times is comparable to writing out the same information out by hand. The difference with the card is that now this information is there for life, instead of for a few days/weeks with writing.

Agree that if we're talking about manual creation of cards, it can be hard to see the ROI given how much effort it typically takes to create high-quality one-off questions and answers.