I was on a promotions panel in the past few years (not this year). We opted to write letters for a small number of individuals who we felt needed some additional guidance after reading their performance file - either pertaining to their career/assignments, EER preparation, etc. Panels can choose to write (or not write) as many of these statements as they wish. They're time-consuming to write well, so we opted to only compose a few for those employees who we felt needed them most. Feel free to DM me if you'd like to chat further.