People who are into running/cycling use "K" a lot, personally I think it's because once someone starts talking in km, if you use miles your stats will look bad by comparison. I know trackers/apps probably had this as default from the start because Europe=metric but so did a lot of satnavs and it didn't change our language in the same way.
It's rare to need kilometres in engineering, but I know from a friend that works at Network Rail that everything is done in kilometres, except final conversions on many older railway lines where the mileposts still measure miles.
Those small blue signs at the side of motorways, and the white emergency location posts, both use kilometres.
Yeah, the thing with imperial units and engineering is that once you get anywhere near mass, weight, force, energy, and all the related units for same, it can get very confusing and error prone. So are we talking pounds-mass, pounds-force, or slugs? (The latter being something that probably no one who didn't take engineering/physics/etc. classes has ever heard of.)
