Oh, I've had this set since 1992-ish. Except the airplane and Suburban, every other vehicle I've had since then has been metric... Volvo-Penta engine in the boat, and cars have been Toyota, Nissan, VW, Audi, or BMW. (BLECH. Wife's choice.) Except for the current Audi which is still under warranty, I do all my own work. If I have not had to use a 16mm in the past 25 years, I doubt I will need it much in the next 25 either. Above 19mm, I do have 22, 24, 30, and 32mm which have seen occasional use, especially the 24.
But yeah, I do like having a complete set even if I have not needed it. Kind of OCD that way... Wife makes fun of me because I hate mismatched sets or sets with things missing. I occasionally audit the silverware drawer and backfill the missing pieces from Ebay...