I have quite a number of metric drill bits and taps, some quite large. I don't recall ever using even one of those.
I got the metric stuff free in the early 1990's. At the time I worked for a Cat attachment and machine conversion plant that is now just another Cat plant after they got bought out. Anyway, at the time, Peoria sent several huge skids of metric drill bits and taps to the plant where I worked in Kansas I think just to unload the stuff. All of it was production quality, and new. Many of the big bits were still in their cardboard tubes! Anyway, it sat around for several years until they decided to just scrap the whole lot of them!
Word went out that any employee wanting some of the bits and taps could take what they wanted of the stuff. For my end, I took everything smaller than approximately 1" in every size that I could dig out. I took multiples of the smaller sizes, every different size I could find. All told maybe 60-75lbs of bits and taps, perhaps much more than that!
I guess I should have tried harder to find applications for them and opportunities to use them. That was the original plan Anyway. Here I am roughly 32 years later and I don't recall ever using even one of them! LOL