What does "For those keeping score, "mean?

For those keeping score, the one useful one is Esuna - Libra, Sight, Teleport and Cure are useless and Cecil's Spirit sucks so Cura is pathetic.

Bir çeviriye bakın

"For those people who want to pay attention to the details" / For those people who have been paying attention to the details"

People who "keep score" in a game, such as soccer or baseball, are people who pay attention to the allotment of points (e.g. usually this is an actual scorekeeper, but it can apply to people who are just watching).

So in this case, the writer is addressing any readers who have been paying close attention to the material discussed previously. Those readers would notice (from analyzing the data) that Esuna is the most useful.