See the image attached - long or complex String.format() expressions may contain quite some %X patterns and lot's of corresponding actual arguments. When it happens - tracking to which %X belongs every actual argument is becoming not very easy, one has to simply do it with his eyes. I think IDEA could help a lot in that point by highlighting the %X portion of the pattern (with a red square border, may be ?) when cursor moves through the actual arguments.
This way "visually binding" every argument to where it belongs in a potentially long and complex pattern will be just a pleasure ..